The next step was to examine the contents of the logs generated at the time of last execution of the purge job and we came across the following: Lets take a quick look at what a block is and why not being able to read it caused the query to fail. After I did REINDEX the problem was solved. How to get rid of black substance in render? Introduction to PostgreSQL REINDEX statement. After a few attempts, we can detect data corruption with the amcheck extension: 1 2 3 4 5 6 7 What went wrong? 2 I've been running a postgres database on an external hard drive and it appears it got corrupted after reconnecting it to a sleeping laptop that THOUGHT the server was still running. Can two electrons (with different quantum numbers) exist at the same place in space? The best time to use this would be a lean period of activity as CREATE INDEX CONCURRENTLY is slowed down with a large number of updates/inserts/deletes on the table when its working. How to optimize the two tangents of a circle by passing through a point outside the circle and calculate the sine value of the angle? or affiliation between Redis and Aiven. With the error pointing to a specific block, its a reasonable possibility that the block itself may be the only corruption in the table, rather than the entire table. 19 I have multiple errors with my postgresql db, which resulted after a power surge: I cannot access most tables from my database. In PostgreSQL, all tables and indexes are stored as a collection of pages; these pages are 8KB by default, though it can be customized during server compile. It was a part of a job that purged older data based on the application need. If not none, corruption checking skips blocks that are marked as all-visible or all-frozen, as specified. purposes only and does not indicate any sponsorship, endorsement What bread dough is quick to prepare and requires no kneading or much skill? Is it okay/safe to load a circuit breaker to 90% of its amperage rating? I could able to connect to DB now! Making statements based on opinion; back them up with references or personal experience. bt_index_check tests that its target, a B-Tree index, respects a variety of invariants. The resulting rows identify the problematic entries, which must be resolved manually by deleting or merging the entries until no duplicates exist. But we still have no clue whether or not the table itself is okay. However if you're building a large index that runs for hours you may wonder if it is 'really' still running. what is difference between na-nimittaggh and animitta? Does the ratio of C in the atmosphere show that global warming is not due to fossil fuels? Which kind of celestial body killed dinosaurs? C. UseCREATE INDEX CONCURRENTLYand drop old/corrupt index: If you are on a version older than 12 your best bet will be to create a new index using CREATE INDEX CONCURRENTLY which will not block you existing operations on the table and then drop the corrupt index using theDROP INDEXdrop the old one. Corruption caused by hypothetical undiscovered bugs in the underlying PostgreSQL access method code, sort code, or transaction management code. We started up recovery cluster with ignore_system_indexes=true setting: pg_ctl -D /data -o '-c ignore_system_indexes=true' restarted dbname=# \c dbname Yay! This page was last edited on 15 March 2023, at 03:10. } Today I encountered a case where a record was missing in query result while existed in the table. auth_delay pause on authentication failure. A. Queries that use indexes are performing more sequential scans. You should really use the latest version. It is an error to specify an endblock outside the range of blocks in the target table. Hmmm. the indexes can be correct, but they can be unbalanced after bulk inserts on many DBMSes. In a replicated configuration, you'll need to check each standby individually, along with the master. All product and service (Please don't share any personal Yes,your index is up to date. Required fields are marked *. bt_index_check and bt_index_parent_check both output log messages about the verification process at DEBUG1 and DEBUG2 severity levels. These include: Structural inconsistencies caused by incorrect operator class implementations. I traced back the problem to probably a corrupted index. Indexes are up to date just after every DML. I believe that a query that scans the whole index e.g. I've posted a related question: It looks like as of postgres 12 you can now, Detect when a CREATE INDEX CONCURRENTLY is finished in PostgreSQL, paquier.xyz/postgresql-2/postgres-12-reindex-concurrently, How to keep your new tool from gathering dust, Chatting with Apple at WWDC: Macros in Swift and the new visionOS, We are graduating the updated button styling for vote arrows, Statement from SO: June 5, 2023 Moderator Action, Dropped an index and recreated it in PostgreSQL 9.2, not used anymore, Is there a way to show the creation statement for an index in PostgreSQL. Filesystems configured to use write barriers plus a storage layer that ignores write barriers. Has there been any change in business logic/table structures? Two weeks back we discovered an ancient bug in PostgreSQL which may cause index corruption when index is built via CREATE INDEX CONCURRENTLY (aka CIC). Hence we can conclude that the query was looking for information in a block [page] but for some reason was not able to read it. This documentation is for an unsupported version of PostgreSQL. How could a radiowave controlled cyborg-mutant be possible? What's the type of this id column and is there any custom code in your postgres installation? Below is a sample of the output: So, our data in the table is fine. Stopping Milkdromeda, for Aesthetic Reasons. In the last few executions of the job, the user saw a major reduction in the number of rows being cleared by the job but none of the usual suspects, like retention rules, had been changed to explain the problem. The job was working fine without any issues on one particular day, but one day it suddenly stopped working. A corruption in the database base often manifests itself in the form of errors when performing a DDL or DML operation on affected relations. So, we decided to convert it into a blog; for as rare as it is for your average PostgreSQL user, our goal is to help you make this elusive problem easier to pin down. Below is a sample of the output: So, our data in the table is fine. In particular, the recovery techniques described there are for recovering what you can from a DB, with the understanding that you'll have missing chunks of data, inconsistent FK relationships, reappearing deleted rows / visible uncommitted rows, and all sorts of problems depending on the repair technique used. By clicking Post Your Answer, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct. More commonly, an inconsistency in the collation order between a primary server and a standby server is implicated, possibly because the major operating system version in use is inconsistent. names used in this website are for identification purposes only If you can afford to have the table locked for a while you can solve it by running: REINDEX INDEX "myIndexName"; The command will rebuild the index getting rid of the error. Checking if a postgres index is up to date? We have enough data to conclude now that there is an issue with the index and it's been corrupted. It was a new record Detecting and fixing corrupted indeces in Postgresql? C. Users complain that some of the data which they are receiving is not what they expect. Find the tables that are corrupted in a Database in postgresql, How to determine PostgreSQL Error Codes from error message, How to make postgres tell which column is causing an error. In addition, it looked like there was also a steady increase in the size of the tables on which the job was running. In this case, its this 8KB page which is referred to as a block in the error. Has there been any change in retention rules? 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So, if theyre likely to happen at some point, and your recovery depends on the ability to detect the problem early, what can you do? Join the FREE newsletter and be part of community with 1000+ memebers. In general, amcheck can only prove the presence of corruption; it cannot prove its absence. The best time to use this would be a lean period of activity as CREATE INDEX CONCURRENTLY is slowed down with a large number of updates/inserts/deletes on the table when it's working. By clicking Post Your Answer, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct. The next step was to examine the contents of the logs generated at the time of last execution of the purge job and we came across the following: Lets take a quick look at what a block is and why not being able to read it caused the query to fail. Automatic verification of the structural integrity of indexes plays a role in the general testing of new or proposed PostgreSQL features that could plausibly allow a logical inconsistency to be introduced. 5mins of Postgres E20: Bug in Postgres 14 with REINDEX / CREATE INDEX CONCURRENTLY & how to resolve Watch on 1 You can check whether the index is being used with EXPLAIN SELECT count (*) FROM my_table WHERE recorded_at > '2018-02-07 23:59:59'; That said, I strongly suspect what you're seeing is the effect of caching the table and/or index. If you see your index in this query it means the index won't work and you have to recreate index. The errors often show up as errors reading tables due to a missing filethat is rather straightforward, of course. Introduction. To fix this we have to rebuild the index and we have a couple of options on how to go about this, each with its own pros and cons: A. Looking at the Postgres database logs, we found something similar to this: We can find out what this file which contains the block actually belongs to by using a query like: Note: In the above query we have ignored the .2 part of file name as only the numbers prior to the . corresponds to the first segment's file name is the same as the filenode. Use REINDEX CONCURRENTLY: This is a better option but is only available in Postgres version 12 onwards. Since pages dont vary in size once its defined during the compilation, these pages are all logically equivalent when were speaking of table pages. Note that amcheck examines a page as represented in some shared memory buffer at the time of verification if there is only a shared buffer hit when accessing the block. Unfortunately, due to the complexity of filesystems (and the storage systems upon which they rely), returning different (corrupt) data is common enough to cause serious problems. Hence we can conclude that the query was looking for information in a block [page] but for some reason was not able to read it. That can detect most cases of data corruption in a given index. Since no error is raised, all indexes tested appear to be logically consistent. Connect and share knowledge within a single location that is structured and easy to search. What could we do next? Join the FREE newsletter and be part of 1000+ member community. To learn more, see our tips on writing great answers. Copyright 1996-2023 The PostgreSQL Global Development Group. All we need to do is rebuild the index to fix the problem. Now we know that the block which could not be read was part of an index which was called in the query. This site requires JavaScript to run correctly. When citing a scientific article do I have to agree with the opinions expressed in the article? Some more vigilant DBAs who keep an eye on pg_stat_user_tables see the idx_scan column increasing at a much slower rate (or not changing at all) when compared to seq_scan. We are going to show how to rebuild the index in the later part of our article. Note. In situations when the index is corrupted or disabled and duplicated physical rows appear in the table, breaking the uniqueness constraint of the index, then index rebuilding with REINDEX will fail. In order to ensure that there is no more than a 2% probability of failure to detect an inconsistency for each heap tuple that should be represented in the index, approximately 2 bytes of memory are needed per tuple. So, we decided to convert it into a blog; for as rare as it is for your average PostgreSQL user, our goal is to help you make this elusive problem easier to pin down. In addition, it looked like there was also a steady increase in the size of the tables on which the job was running. No error concerning corruption raised by amcheck should ever be a false positive. How do I figure when an index was last used? amcheck can be effective at detecting various types of failure modes that data checksums will fail to catch. How to check contents of an index in a database? Asking for help, clarification, or responding to other answers. sfsi_widget_set(); The good news? How to check if postgres is indexing concurrently? How to optimize the two tangents of a circle by passing through a point outside the circle and calculate the sine value of the angle? It also will place an exclusive lock on the index thats benign processed; this means that even read attempts on that index will fail during this operation. What's the point of certificates in SSL/TLS? - Daniel Vrit Jan 15, 2014 at 18:58 Please show the \d+ for the table widgets, and explain for both with-index and without-index plans. UseREINDEX CONCURRENTLY: This is a better option but is only available in Postgres version 12 onwards. 1. I think you need to diagnose and fix this fundamentally and not try to band aid it in your query. bt_index_check acquires an AccessShareLock on the target index and the heap relation it belongs to. A reliable method to check table sanity is to do a pg_dump of the table to which the index belongs, as pg_dump doesnt use any indexes but reads the table data directly. It only takes a minute to sign up. Make a file-system-level copy of your database before attempting any repair. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. This blog post was co-authored by Ajay Patel and Deepanshu Sharma. As no errors were logged during job execution, we started looking at DB logs for any errors/warnings. There is a tutorial for setting them up. Can you guys please suggest something to find the corrupted or unusable indexes in postgresql. Can a pawn move 2 spaces if doing so would cause en passant mate? adminpack pgAdmin support toolpack, F.3. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. It might be caused by poor administrative actions like kill -9 of any of Postgres processes etc. The high level principle behind heapallindexed verification is that a new index that is equivalent to the existing, target index must only have entries that can be found in the existing structure. What could we do next? F.1. The best answers are voted up and rise to the top, Not the answer you're looking for? Next, step would be to force the query to hit the table directly and see if the results are any different. More often than not to find if indeed there is index corruption, one needs to observe the behavior (execution times) and results of the queries themselves. A reliable method to check table sanity is to do a pg_dump of the table to which the index belongs, as pg_dump doesnt use any indexes but reads the table data directly. Corruption caused by faulty RAM, or the broader memory subsystem. Note:If you wish to get more information on the structure of a page in PostgreSQL please refer toDatabase Page Layoutsection of the PostgreSQL documentation. No? M3, M3 Aggregator, M3 Coordinator, This is a rather typical situation that the first execution of a query is much slower than the next ones. The summarizing structure fingerprints every tuple found within the target index. Since pages dont vary in size once its defined during the compilation, these pages are all logically equivalent when were speaking of table pages. See Section38.16.3 for details of operator class support functions. The database is still up and running, connectivity is intact, applications are running fine. Do characters suffer fall damage in the Astral Plane? It was a part of a job that purged older data based upon the application need. A ShareLock is required on the target index by bt_index_parent_check (a ShareLock is also acquired on the heap relation). It is an error to specify a startblock outside the range of blocks in the target table. Usually, the community announces a minor version update on the second Tuesday of the second month of . trademarks of the Apache Software Foundation in the United States A REINDEX may not be effective in repairing corruption. Our user had a query that was a part of his regular workflow. Remember that most corruption is caused by hardware issues: RAID controllers with faulty / worn out battery backup, and an unexpected power loss Hard disk drives with write-back cache enabled, and an unexpected power loss Cheap SSDs with insufficient power-loss protection, and an unexpected power-loss Defective RAM version on Github that targets earlier PostgreSQL versions, more specialized tool for verifying the integrity of the visibility map, called pg_visibility, full barrier support was added by Liunx 2.6.33-rc1, Christophe Pettus's FOSDEM presentation on database corruption, https://wiki.postgresql.org/index.php?title=Corruption&oldid=37662, RAID controllers with faulty / worn out battery backup, and an unexpected power loss, Hard disk drives with write-back cache enabled, and an unexpected power loss, Cheap SSDs with insufficient power-loss protection, and an unexpected power-loss. One obvious testing strategy is to call amcheck functions continuously when running the standard regression tests. People often destroy potentially recoverable data by trying to repair it. This can be done by setting parameter . If left undetected, it could not only lead to wrong answers, it can also end up being copied during a base backup (affecting backups and replication). Note that the function holds locks only while running, not for the entire transaction. If specified, corruption checking ends at the specified block, skipping all remaining blocks. Also there is the REINDEX command if you think, that your index is corrupted. This can be done by setting parameter enable_indexscan parameter to off in the psql session and executing the query again: If there is a difference in the output in this case row count (7 with Index Scan and 12 with Sequential scan), you have every reason to believe something is wrong with your index. How do I write such query? When you dump the table and press it to another database or transfer the table to another table by changing its name, the data comes back healthy. To solve such a problem, youll first need to remove the duplicated rows from the table before attempting to rebuild the index. In some cases, it can be useful to manually build a second index concurrently alongside the old index and then remove the old index: all indexes in the entire database (REINDEX DATABASE). This can be done by setting parameter enable_indexscanparameter to off in the psql session and executing the query again: If there is a difference in the output in this case row count (7 with Index Scan and 12 with Sequential scan), you have every reason to believe something is wrong with your index. Find centralized, trusted content and collaborate around the technologies you use most. Find centralized, trusted content and collaborate around the technologies you use most. pageinspect may play a useful role in diagnosing corruption that amcheck detects. What was the point of this conversation between Megamind and Minion? When the heapallindexed argument to B-Tree verification functions is true, an additional phase of verification is performed against the table associated with the target index relation. bt_index_check does not verify invariants that span child/parent relationships, but will verify the presence of all heap tuples as index tuples within the index when heapallindexed is true. Your email address will not be published. Here you can find all things Postgres Pulse, including all of our blog postsandour YouTube series. If there is no lock it implies that either the index has finished building, or the create failed and left an invalid index. It should only be run against a copy of the database. Don't do REINDEX. Verification of table structure and associated visibility and transaction status information plays a similar role. Has there been any change in business logic/table structures? Cut the release versions from file in linux. It is impossible for me to know if there are missing records. Our user had a query which was a part of his regular workflow. How to keep your new tool from gathering dust, Chatting with Apple at WWDC: Macros in Swift and the new visionOS, We are graduating the updated button styling for vote arrows, Statement from SO: June 5, 2023 Moderator Action. Description REINDEX rebuilds an index using the data stored in the index's table, replacing the old copy of the index. By clicking Post Your Answer, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct. Remember that most corruption is caused by hardware issues: Consider contacting a professional support service provider. The database is still up and running, connectivity is intact, and applications are running fine. 2 Answers Sorted by: 7 New data gets indexed automatically. A. Queries that use indexes are performing more sequential scans. bt_index_parent_check tests that its target, a B-Tree index, respects a variety of invariants. We have no errors, the query runs fine, but the user insists that the data returned is not correct. Why isnt it obvious that the grammars of natural languages cannot be context-free? Asking for help, clarification, or responding to other answers. Has there been any change in retention rules? Cleanup of broken FSM files. C. Users complain that some of the data which they are receiving is not what they expect. So, if theyre likely to happen at some point, and your recovery depends on the ability to detect the problem early, what can you do? These will rewrite the database files in place. The following optional arguments are recognized: If true, corruption checking stops at the end of the first block in which any corruptions are found. Is there a way to get a notification when an index is corrupted? File system or storage subsystem faults where checksums happen to simply not be enabled. As less memory is made available per tuple, the probability of missing an inconsistency slowly increases. Learn more about Stack Overflow the company, and our products. Likewise, when I sort with order by in the relevant column, the data is missing. A UNIQUE index works on top of one or more columns whose combination is unique in a table. See Section33.1 for details on running the tests. B. Verification of the presence of heap tuples as index tuples is requested for the subset that are unique indexes. We are going to show how to rebuild the index in the later part of our article. Symptoms of heap corruption can be subtle. If possible, put a copy of it on an external hard drive, DVD, or other storage you can disconnect from your computer so you don't accidentally modify your snapshot after making it. How to start building lithium-ion battery charger? For tables with an extremely high volume of transactions, you have to be very careful about adding indexes. Example usage: This example shows a session that performs verification of the 10 largest catalog indexes in the database test. Create MD5 within a pipe without changing the data stream, Cut the release versions from file in linux. For more details please refer toDatabase File Layoutin the PostgreSQL documentation. The job was working fine without any issues on one particular day, but one day it suddenly stopped working. These messages provide detailed information about the verification process that may be of interest to PostgreSQL developers. This kind of corruption can also be detected with data page checksums. To learn more, see our tips on writing great answers. Adding an index without a lag (PostgreSQL). It was a part of a job that purged older data based upon the application need. So, if theyre likely to happen at some point, and your recovery depends on the ability to detect the problem early, what can you do? The thing is that when runing a query I get results.. What are some of the symptoms of a corrupt index you might see in a database? if (typeof sfsi_widget_set == "function") { PostgreSQL 12 and above have the ability to do pg_checksums. execution: count = 8,756,237 execution time = ~3 seconds, First execution: count = 6,487,274 execution time = ~4 minutes, Second execution: count = 6,487,274 execution time = ~3 seconds. A. Queries that use indexes are performing more sequential scans. Checks a table, sequence, or materialized view for structural corruption, where pages in the relation contain data that is invalidly formatted, and for logical corruption, where pages are structurally valid but inconsistent with the rest of the database cluster. Lets add a hypothetical but a possible twist where there were no errors in the logs. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. The job was working fine without any issues on one particular day, but one day it suddenly stopped working. Corrupt relations are most concerning in live production environments, precisely the same environments where high risk activities are least welcome. As such, this kind of corruption cannot be detected with checksums. How to keep your new tool from gathering dust, Chatting with Apple at WWDC: Macros in Swift and the new visionOS, We are graduating the updated button styling for vote arrows, Statement from SO: June 5, 2023 Moderator Action, PostgreSQL Database Data File Integrity Check. With the list of corrupted FSM files in hand, stop the . Offline index rebuild - does it also create a whole new copy of the index? A corruption in the database base often manifests itself in the form of errors when performing a DDL or DML operation on affected relations. Since pages dont vary in size once its defined during the compilation, these pages are all logically equivalent when were speaking of table pages. Is id an integer / bigint? Read the Guide_to_reporting_problems and post to the pgsql-general mailing list with information about the problem. For more details please refer to, Next, step would be to force the query to hit the table directly and see if the results are any different. As a result, there may be different types of pages in a single index. PostgreSQL relies heavily on the filesystem returning the same data that was previously written. It also will place an exclusive lock on the index thats benign processed; this means that even read attempts on that index will fail during this operation. However, ECC memory is typically only immune to single-bit errors, and should not be assumed to provide absolute protection against failures that result in memory corruption. Index corruption is very bad problem. All we need to do is rebuild the index to fix the problem. C. Use CREATE INDEX CONCURRENTLY and drop old/corrupt index: If you are on a version older than 12 your best bet will be to create a new index using CREATE INDEX CONCURRENTLY which will not block you existing operations on the table and then drop the corrupt index using the DROP INDEX drop the old one. What is a collation? *Redis is a registered trademark of Redis Ltd. Any rights therein If the unique_route_index is corrupted, you can find duplicated rows in the route table by issuing the following query: SELECT source, destination, count FROM (SELECT source, destination, COUNT(*) AS count FROM route GROUP BY source, destination) AS foo WHERE count > 1; and/or other countries. "Murder laws are governed by the states, [not the federal government]." "Corruption" can cover many different things, though, and some damage would not be detected by simply using the index. To fix this we have to rebuild the index and we have a couple of options on how to go about this, each with its own pros and cons: A. This is running on AWS Aurora postgres with an r4.xlarge instance. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. If you are worried about this, you can run it routinely to search for system catalog corruption that might otherwise go undetected. In the last few executions of the job, the user saw a major reduction in the number of rows being cleared by the job but none of the usual suspects, like retention rules, had been changed to explain the problem. The summarizing structure is bound in size by maintenance_work_mem. Although the corruption reports generated by these functions do not focus on the contents of the corrupted data so much as on the structure of that data and the nature of the corruptions found, an attacker who gains permission to execute these functions, particularly if the attacker can also induce corruption, might be able to infer something of the data itself from such messages. Stop the postmaster and take a file system level copy of your database NOW!. As a result, there may be different types of pages in a single index. Is Vivek Ramaswamy right? Permission to execute amcheck functions may be granted to non-superusers, but before granting such permissions careful consideration should be given to data security and privacy concerns. Having the damaged data may be the only way to figure out why it was damaged and how to prevent the same thing happening again. Does the ratio of C in the atmosphere show that global warming is not due to fossil fuels? If two asteroids will collide, how can we call it? The correctness of the access method functions behind index scans and other important operations relies on these invariants always holding. We could generate the querys explain analyze plan, which should show where it is getting its data from. In PostgreSQL, can you read from an index during a ALTER INDEX SET TABLESPACE operation? document.getElementById( "ak_js_1" ).setAttribute( "value", ( new Date() ).getTime() ); window.addEventListener("sfsi_functions_loaded", function() On June 16 2022, a new PostgreSQL 14 minor release will be published by the PostgreSQL Global Development Group. We have enough data to conclude now that there is an issue with the index and it's been corrupted. Note that when checksums are enabled, amcheck may raise an error due to a checksum failure when a corrupt block is read into a buffer. PostgreSQL does not protect against correctable memory errors and it is assumed you will operate using RAM that uses industry standard Error Correcting Codes (ECC) or better protection. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Though rare, updates to operating system collation rules can cause these issues. { Next question, please! In Situation C, this behavior guides us more toward a corrupt index, but its hard to know for sure without more knowledge; this is one scenario where the Google and go approach often yields very little for anyone hunting for an answer to their challenge. You can rebuild corrupted indexes that do not have UNIQUE in their definition using the following command, that creates a new index replacing the old one: Re-indexing applies locks to the table and may interfere with normal use of the database. Trial 3: Let's try to reindex the database Unlike the B-Tree checking functions which report corruption by raising errors, the heap checking function verify_heapam checks a table and attempts to return a set of rows, one row per corruption detected. As a result, there may be different types of pages in a single index. Throughout all strategies, caution is the best characteristic you can use to ensure the survival of your data and your peace of mind! Comparisons of datums of a collatable type like text must be immutable (just as all comparisons used for B-Tree index scans must be immutable), which implies that operating system collation rules must never change. Our user had a query which was a part of his regular workflow. When heapallindexed verification is performed, there is generally a greatly increased chance of detecting single-bit errors, since strict binary equality is tested, and the indexed attributes within the heap are tested. The best time to use this would be a scheduled downtime or lean period of activity. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. bt_index_check and bt_index_parent_check both output log messages about the verification process at DEBUG1 and DEBUG2 severity levels. > I would like to detect some of the following DB corruptions: > - corruption in DB indexes A query that scans the whole index (say, to sort on it) should generally find damaged pages in indexes. We are going to show how to rebuild the index in the later part of our article. To learn more, see our tips on writing great answers. It looks as if the index is corrupted as soon as it's created. More often than not to find if indeed there is index corruption, one needs to observe the behavior (execution times) and results of the queries themselves. There were numerous bug fixes after 9.3.3., especially one in 9.3.4 that would prevent index corruption. . Postgresql - measuring performance and how to tell whether indexes should be refreshed. More often than not to find if indeed there is index corruption, one needs to observe the behavior (execution times) and results of the queries themselves. For most tables in most systems this is not an issue. Why isnt it obvious that the grammars of natural languages cannot be context-free? As no errors were logged during job execution, we started looking at DB logs for any errors/warnings. Lets add a hypothetical but possible twist where there were no errors in the logs. The experimental hex editor toolkit pg_hexedit can be used for low-level analysis of PostgreSQL relation files. Is it normal for spokes to poke through the rim this much? Examples include toasted values in the main table which lack a corresponding entry in the toast table, and tuples in the main table with a Transaction ID that is older than the oldest valid Transaction ID in the database or cluster. C. Use CREATE INDEX CONCURRENTLY and drop old/corrupt index: If you are on a version older than 12 your best bet will be to create a new index using CREATE INDEX CONCURRENTLY which will not block you existing operations on the table and then drop the corrupt index using the DROP INDEX drop the old one. It wont re-create the index concurrently, it will lock the table for writes while the index is being created, the best solution is to drop the invalid index and recreate it with CONCURRENTLY flag. The good news? Verification is performed using the same procedures as those used by index scans themselves, which may be user-defined operator class code. to reach us.). Structural corruption can happen due to faulty storage hardware, or relation files being overwritten or modified by unrelated software. rev2023.6.12.43489. The best you can do is pg_dump -f /dev/null dbname This will read all tables and throw an error at the first corruption that causes an error. Asking for help, clarification, or responding to other answers. Connect and share knowledge within a single location that is structured and easy to search. The answer isnt just one thing, but many: Monitoring, checksums, and pg_catcheck are a few ways you can catch the problem as it occurs. After I did REINDEX the problem was solved. Join us on Monday, May 11th, for our next Pulse Live Session! As of PostgreSQL 10, there is am extension called amcheck. Does the policy change for AI-generated content affect users who (want to) How can i check in Postgresql if specific index is loaded to memory? Optionally, when the heapallindexed argument is true, the function verifies the presence of all heap tuples that should be found within the index. A film where a guy has to convince the robot shes okay, Cutting wood with angle grinder at low RPM, First execution: count = 8,756,237 execution time = ~5 minutes, Second Making statements based on opinion; back them up with references or personal experience. A corruption in the database base often manifests itself in the form of errors when performing a DDL or DML operation on affected relations. Has there been any change in business logic/table structures? An explanation for the root cause of an invariant violation should be sought. Does the policy change for AI-generated content affect users who (want to) Postgresql Select based on primary key return null, What are the available options to identify and remove the invalid objects in Postgres (ex: corrupted indexes), debugging postgres 9.0.1 table corruption, How do I repair a corrupted system table in PostgreSQL. PG Phriday: Addressing Demands of Highly Available OLTP Environments, Explaining the PostgreSQL Query Optimizer with Bruce MomjianBeyond Joins and Indexes: Webinar Recap, Processing PostgreSQL JSON & JSONB data in Java, Professional Services, Support and Training Overview. 7 Today I encountered a case where a record was missing in query result while existed in the table. Why should the concept of "nearest/minimum/closest image" even come into the discussion of molecular simulation? Where can one find the aluminum anode rod that replaces a magnesium anode rod? Valid options are all-visible, all-frozen and none. A. Queries that use indexes are performing more sequential scans. In this article I'll talk about the problem we need to solvethat PostgreSQL indexes can get corrupted by changes in collations that occur naturally over timeand how the new feature will make things better in a future version of PostgreSQL. Naturally, this query could easily be changed to call bt_index_check for every index in the database where verification is supported. Bringing your environment back to good health, however, depends on the things weve talked about in prior posts: PITR backups and the WAL stream, standby servers, and delayed standby servers can all help in various ways to rescue you from the problem when you do hit it. By clicking Post Your Answer, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct. What went wrong? The overall chances of any DBA never running into corruption is rare. Any single absent or malformed tuple has a new opportunity to be detected with each new verification attempt. Thanks for contributing an answer to Database Administrators Stack Exchange! Is Vivek Ramaswamy right? Tip. If you suspect that your system catalogs are corrupted, this tool may help you figure out exactly what problems you have and how serious they are. For more details please refer to Database File Layout in the PostgreSQL documentation. In this case, it's this 8KB page which is referred to as a block in the error. Or something else? Corruption issues can be time consuming and difficult to diagnose and fix, and are often hardware- or configuration-specific. Does this difference in execution time indicate that the index is not being updated correctly? Access to catalog tables is performed and could be problematic if the catalogs themselves are corrupted. are reserved to Redis Ltd. Any use by Aiven is for referential Throughout all strategies, caution is the best characteristic you can use to ensure the survival of your data and your peace of mind! While a CHECK constraint that violates this rule may appear to work in simple tests, it cannot guarantee that the database will not reach a state in which the constraint condition is false (due to subsequent changes of the other row(s) involved). Click here. This lock mode is the same lock mode acquired on relations by simple SELECT statements. Although it only verifies the integrity of B-Tree indexes, it is reasonably well suited for use as a general purpose corruption smoke test, especially because the indexes can be verified against the heap with the "heapallindexed" verification option (later versions only). It cannot guard against all causes of backend crashes, as even executing the calling query could be unsafe on a badly corrupted system. B. Kubernetes are trademarks and property of their respective owners. Now, log in and get the result. In situations A and B, for the majority of the cases, you could easily be misled to the conclusion that your statistics were out of date. The bug could be a source of index corruption reports that we receive from the field once in awhile. So you know the index is done when your query returns. The errors often show up as errors reading tables due to a missing filethat is rather straightforward, of course. Thanks for contributing an answer to Stack Overflow! Please, Note:If you wish to get more information on the structure of a page in PostgreSQL please refer to, Note: In the above query we have ignored the .2 part of file name as only the numbers prior to the . corresponds to the first segment's file name is the same as the filenode. Repairing Corruption The amcheck module provides functions that allow you to verify the logical consistency of the structure of relations. Throughout all strategies, caution is the best characteristic you can use to ensure the survival of your data and your peace of mind! In practice, an index can become corrupted and no longer contains valid data due to hardware failures or software bugs. You can ask your questions via email at postgrespulse@enterprisedb.com, hashtag on Twitter, or live during the event right here. B. B. With the error pointing to a specific block, its a reasonable possibility that the block itself may be the only corruption in the table, rather than the entire table. rev2023.6.12.43489. Connect and share knowledge within a single location that is structured and easy to search. It might save your data. A film where a guy has to convince the robot shes okay. To learn more, see our tips on writing great answers. For more details please refer to Database File Layout in the PostgreSQL documentation. Some more vigilant DBAs who keep an eye on pg_stat_user_tables see the idx_scan column increasing at a much slower rate (or not changing at all) when compared to seq_scan Making statements based on opinion; back them up with references or personal experience. rev2023.6.12.43489. This can be done by setting parameter enable_indexscan parameter to off in the psql session and executing the query again: If there is a difference in the output in this case row count (7 with Index Scan and 12 with Sequential scan), you have every reason to believe something is wrong with your index. These cases may involve an incorrectly implemented B-Tree operator class used by the index that is checked, or, hypothetically, undiscovered bugs in the underlying B-Tree index access method code. Not the answer you're looking for? As the table check_corruption data file is 16490, I am going to corrupt the file with the Operating system's dd command. That is a major problem because users will get a false sense of confidence relying on their backup schedule. Stack Exchange network consists of 181 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers. Anything specific you want to share? PostgreSQL REINDEX command rebuilds an existing index or all indexes for a table or entire database. Copyright However, there is no change to the relation-level locks acquired when heapallindexed verification is performed. This approach limits the overhead of verification significantly, while only slightly reducing the probability of detecting a problem, especially for installations where verification is treated as a routine maintenance task. Where can one find the aluminum anode rod that replaces a magnesium anode rod? These locks prevent concurrent data modification from INSERT, UPDATE, and DELETE commands. We make use of the problems we solve and the conversations we have in helping people with Postgres; while this scenario was one we see less often, its one for which we find the solution to be particularly useful to those who do encounter the invisible cost of index corruption. bt_index_parent_check can be thought of as a more thorough variant of bt_index_check: unlike bt_index_check, bt_index_parent_check also checks invariants that span parent/child relationships, including checking that there are no missing downlinks in the index structure. Given a table with around 5 million records added per month, this simple query has vastly different run times from the first execution to the 2nd: There is an index on the field recorded_at. All supported releases of PostgreSQL are affected by this bug. Stopping Milkdromeda, for Aesthetic Reasons. 1 Answer Sorted by: 2 It looks like an on disk index corruption. 20 If I create an index CONCURRENTLY in PostgreSQL, how can I see when it is finished? How should I designate a break in a sentence to display a code segment? Apache, Apache Kafka, Kafka, Apache Flink, Flink, Apache The best time to use this would be a lean period of activity as CREATE INDEX CONCURRENTLY is slowed down with a large number of updates/inserts/deletes on the table when it's working. Also, if the toast table or its index is corrupt, checking it against toast values could conceivably crash the server, although in many cases this would just produce an error. How to keep your new tool from gathering dust, Chatting with Apple at WWDC: Macros in Swift and the new visionOS, We are graduating the updated button styling for vote arrows, Statement from SO: June 5, 2023 Moderator Action. It is unlikely on this basis to believe that the data is damaged or obsolete in any way. For example, certain functions verify, among other things, that all B-Tree pages have items in logical order (e.g., for B-Tree indexes on text, index tuples should be in collated lexical order). To your question: there is no verifier tool AFAIK. How to detect corrupted indexes in PostgreSQL? How to ask Postgres to report broken value? Trying to restore a corrupt Postgresql database, with corrupt data folder. Is the function for the Weak Goldbach Conjecture an increasing function? rev2023.6.12.43489. Thanks for contributing an answer to Stack Overflow! Detecting storage layer corruption inside PostgreSQL as early as possible is important. When I try for example select * from ac_cash_collection, I get the foolowing error: ERROR: missing chunk number 0 for toast value 118486855 in pg_toast_2619 when I try pg_dump I get the following error: In situations A and B, for the majority of the cases, you could easily be misled to the conclusion that your statistics were out of date. and drop old/corrupt index: If you are on a version older than 12 your best bet will be to create a new index using CREATE INDEX CONCURRENTLY which will not block you existing operations on the table and then drop the corrupt index using the. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. [postgres@stagdb 13455]$ dd bs=8192 count=1 seek=1 of=16490 if=16490. If you're mounted and forced to make a melee attack, do you attack your mount? The thing is that normally when I run reports I get more than a 10000 records. It only takes a minute to sign up. Some more vigilant DBAs who keep an eye on pg_stat_user_tables see the idx_scan column increasing at a much slower rate (or not changing at all) when compared to seq_scan. Is understanding classical composition guidelines beneficial to a jazz composer? Looking at the Postgres database logs, we found something similar to this: We can find out what this file which contains the block actually belongs to by using a query like: Note:In the above query we have ignored the .2 part of file name as only the numbers prior to the . corresponds to the first segments file name is the same as the filenode. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. parameter to off in the psql session and executing the query again: : This is a better option but is only available in Postgres version 12 onwards. Has there been any change in retention rules? Have there been any bulk operations, like data load or truncate? In Situation C, this behavior guides us more toward a corrupt index, but its hard to know for sure without more knowledge; this is one scenario where the Google and go approach often yields very little for anyone hunting for an answer to their challenge. Your email address will not be published. REINDEX INDEX idx_users_on_display_name; reindexes index idx_users_on_display_name. But we still have no clue whether or not the table itself is okay. Remember that your hardware settings and postgresql configuration are vital information, as are any error messages, your Pg version, etc. Is the Sun hotter today, in terms of absolute temperature (i.e., NOT total luminosity), than it was in the distant past? For more information on the REINDEX command, see the PostgreSQL documentation page. "Murder laws are governed by the states, [not the federal government]." 1 $ pgbench -c 5 -T 3600 Creating a corrupt database by setting fsync = off Let's set fsync = off in postgresql.conf and power off the server while it is under load. In this case I suspect the primary key is corrupt. How to connect two wildly different power sources? Replication Server 7 vs Postgres Distributed 5.0: Which Offers Better Performance and Scalability? For example, the following route table has a unique_route_index index defining unique rows based on the combination of the source and destination columns: If the unique_route_index is corrupted, you can find duplicated rows in the route table by issuing the following query: The above query groups the data by the same source and destination fields defined in the index, and filters any entries with more than one occurrence. We have enough data to conclude now that there is an issue with the index and its been corrupted. The best time to use this would be a scheduled downtime or lean period of activity. For this reason, verify_heapam has been designed to diagnose corruption without undue risk. PostgreSQL 9.6 introduced a more specialized tool for verifying the integrity of the visibility map, called pg_visibility. I am attempting to rebuild indexes to solve index bloat, and I need to keep the old index around for a while until the new one has finished, so I need to know when it's finished. The new PostgreSQL 14.4 release fixes an issue with all versions of PostgreSQL 14 that can lead to silent corruption of indexes. A reliable method to check table sanity is to do a pg_dump of the table to which the index belongs, as pg_dump doesnt use any indexes but reads the table data directly. However, a corrupt index is not as obvious as a corrupt table. For each corruption detected, verify_heapam returns a row with the following columns: The number of the block containing the corrupt page. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Advanced users may also find this information helpful, since it provides additional context should verification actually detect an inconsistency. Your backup copy is also important evidence that may help figure out what caused the problem, allowing you to prevent it from happening again. Don't use pg_dump, instead make a copy of all the files in the data directory (the one that contains the "base", "pg_xlog", "pg_clog" etc folders). Want to edit, but don't see an edit button when logged in? However, a corrupt index is not as obvious as a corrupt table. More often than not to find if indeed there is index corruption, one needs to observe the behavior (execution times) and results of the queries themselves. PostgreSQL does not support CHECK constraints that reference table data other than the new or updated row being checked. All default PostgreSQL DB parameter groups have an rds.adaptive_autovacuum parameter that's set to 1, thus activating the feature. The database is still up and running, connectivity is intact, applications are running fine. Repair efforts usually destroy that evidence. Relation pages which are correctly formatted, internally consistent, and correct relative to their own internal checksums may still contain logical corruption. However, with an index, the first page is normally reserved as a metapage; the difference is that it carries control information within it. What proportion of parenting time makes someone a "primary parent"? How could a radiowave controlled cyborg-mutant be possible? Is there a way to tell how postgresql uses an index? Why have God chosen to order offering Isaak as a whole-burnt offering to test Abraham? By Lukas Fittl June 02, 2022 Today, we're going to talk about an important indexing bug that was discovered in Postgres 14 and how you can verify if this affects you with the amcheck extension. Functions F.2.2. Transformer winding voltages shouldn't add in additive polarity? Is the Sun hotter today, in terms of absolute temperature (i.e., NOT total luminosity), than it was in the distant past? In the last few executions of the job, the user saw a major reduction in the number of rows being cleared by the job but none of the usual suspects, like retention rules, had been changed to explain the problem. Run the bt_index_parent_check function from the amcheck extension. If I create an index CONCURRENTLY in PostgreSQL, how can I see when it is finished? Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. OpenSearch, PostgreSQL, MySQL, InfluxDB, Grafana, Terraform, and Next, step would be to force the query to hit the table directly and see if the results are any different. dd bs=8192 count=1 seek=1 of=16490 if=16490. Using amcheck Effectively F.2.4. With the error pointing to a specific block, its a reasonable possibility that the block itself may be the only corruption in the table, rather than the entire table. bt_index_parent_check follows the general convention of raising an error if it finds a logical inconsistency or other problem. As no errors were logged during job execution, we started looking at DB logs for any errors/warnings. Use REINDEX name: Using this will allow reads, but locks all writes of the indexs parent table. In addition, it looked like there was also a steady increase in the size of the tables on which the job was running. B. The answer isnt just one thing, but many: Monitoring, checksums, and pg_catcheck are a few ways you can catch the problem as it occurs. However, with an index, the first page is normally reserved as a metapage; the difference is that it carries control information within it. It is impossible for me to know if there are missing records. Lets add a hypothetical but a possible twist where there were no errors in the logs. pg_catcheck is a simple tool for diagnosing system catalog corruption. Not the answer you're looking for? The overall chances of any DBA never running into corruption is rare. 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Create a whole new copy of the structure of relations underlying PostgreSQL access method behind... Corruption checking skips blocks that are unique indexes single absent or malformed has. Not none, corruption checking ends at the specified block, skipping all remaining blocks will fail to catch a! If there are missing records query result while existed in the logs page was last?. Hours you may wonder if it finds a logical inconsistency or other problem INSERT update... Verification attempt containing the corrupt page be used for low-level analysis of PostgreSQL 10, is! Be read was part of a job that purged older data based upon application... Alter index SET TABLESPACE operation Isaak as a corrupt table sense of confidence postgres check if index is corrupted! Remember that your hardware settings and PostgreSQL configuration are vital information, as specified postgrespulse @,... Fix this fundamentally and not try to band aid it in your returns. Wonder if it is impossible for me to know if there are missing records and could be scheduled! Where it is finished it also create a whole new copy of database! Member community think you need to diagnose and fix, and DELETE commands making based. Release versions from file in linux no error is raised, all indexes appear! To test Abraham show where it is an issue specialized tool for verifying the of! Here you can find all things Postgres Pulse, including all of our article easily be changed call! Probability of missing an inconsistency their own internal checksums may still contain logical corruption change in business logic/table structures postgres check if index is corrupted... Heap tuples as index tuples is requested for the root cause of an index was edited. Refer toDatabase file Layoutin the PostgreSQL documentation without undue risk I sort with order in... Your RSS reader no kneading or much skill command rebuilds an existing index or all tested. A large index that runs for hours you may wonder if it is?... Method functions behind index scans themselves, which may be user-defined operator implementations. More details please refer to database file Layout in the PostgreSQL documentation during! Users will get a notification when an index CONCURRENTLY in PostgreSQL proportion of parenting time makes someone a `` parent. 'Really ' still running including all of our article through the rim this?... Collaborate around the technologies you use most lead to silent corruption of indexes bulk. Blocks that are unique indexes fix this fundamentally and not try to band aid in... And above have the ability to do is rebuild the index is corrupted file linux. These issues opinion ; back them up with references or personal experience most! Corruption that might otherwise go undetected PostgreSQL, can you guys please something. Execution, we started looking at DB logs for any errors/warnings corruption issues can effective... We receive from the table itself is okay a magnesium anode rod that replaces a anode! Gets indexed automatically whose combination is unique in a single location that is a sample of Apache. Subset that are marked as all-visible or all-frozen, as are any error messages, your index in the base. Failed and left an invalid index that there is the REINDEX command, see our on... The general convention of raising an error to specify a startblock outside the range of blocks the. For spokes to poke through the rim this much found within the target.! Performing a DDL or DML operation on affected relations you & # x27 ; s created using this will reads. Rare, updates to operating system collation rules can cause these issues expressed the! Resulting rows identify the problematic entries, which should show where it is getting data... Collation rules can cause these issues the filenode CC BY-SA example usage: this is a sample of database! Pages which are correctly formatted, internally consistent, and our products great answers 20 if I create an without! On top of one or more columns whose combination is unique in table! Destroy potentially recoverable data by trying to repair it '' ) { PostgreSQL and! More about Stack Overflow the company, and our products paste this into! However if you are worried about this, you have to agree with following. Faults where checksums happen to simply not be detected with data page checksums - measuring performance and how to how. Agree with the opinions expressed in the relevant column, the data is missing So our., step would be a source of index corruption reports that we receive the! This example shows a session that performs verification of the presence of heap as... Issues: Consider contacting a professional support service provider it should only be run against a of. File Layoutin the PostgreSQL documentation verification attempt bulk inserts on many DBMSes provides! It 's this 8KB page which is referred to as a corrupt table, applications are fine! Missing in query result while existed in the later part of an index become. Every index in the PostgreSQL documentation the filesystem returning the same data that was previously written Users! Display a code segment ]. any single absent or malformed tuple has a opportunity... Simply not be context-free tuple has a new record detecting and fixing corrupted indeces in PostgreSQL, how we... Robot shes okay with coworkers, Reach developers & technologists share private knowledge with coworkers, Reach developers & share. Page checksums toolkit pg_hexedit can be used for low-level analysis of PostgreSQL 10, there is no lock it that... Logically consistent B-Tree index, respects a variety of invariants memory subsystem play a useful role in corruption... Obvious as a block in the table it implies that either the index fix. Its amperage rating personal experience marked as all-visible or all-frozen, as specified a logical inconsistency or problem... Second month of returned is not an issue with the opinions expressed in the target index with.... Hypothetical undiscovered bugs in the later part of his regular workflow which the job was working without. Are vital information, as are any different system catalog corruption the Guide_to_reporting_problems and post to the top, for. Actions like kill -9 of any of Postgres processes etc and you have to index... Variety of invariants be context-free the following columns: the number of the indexs parent table is no lock implies. Of raising an error to specify a startblock outside the range of in... And DELETE commands coworkers, Reach developers & technologists worldwide of `` nearest/minimum/closest image '' even come the. Target index and it 's been corrupted top, not the answer you 're for. Itself in the relevant column, the community announces a minor version update the! Table structure and associated visibility and transaction status information plays a similar role no it. Stagdb 13455 ] $ dd bs=8192 count=1 seek=1 of=16490 if=16490 implies that either the index corrupted... The whole index e.g a magnesium anode rod a scientific article do I figure when an CONCURRENTLY. The postgres check if index is corrupted map, called pg_visibility specific problem with enough detail to identify an answer... A storage layer corruption inside PostgreSQL as early as possible is important strategies, caution is REINDEX. A possible twist where there were no errors in the later part of his regular workflow believe that query... Data checksums will fail to catch but one day it suddenly stopped working as! See the PostgreSQL documentation the entries until no duplicates exist of errors when performing a DDL or DML operation affected. Call amcheck functions continuously when running the standard regression tests resulting rows identify the problematic entries, which must resolved. N'T add in additive polarity runs fine, but one day it suddenly stopped working not what they expect you... Relies heavily on the target table no lock it implies that either the index the... Not postgres check if index is corrupted to band aid it in your query information, as specified have... At 03:10. and could be a source of index corruption reports that receive... Of corrupted FSM files in hand, stop the PostgreSQL 10, there may of! Never running into corruption is caused by hardware issues: Consider contacting a professional support provider. Reindex command, see our tips on writing great answers think, that hardware! Rds.Adaptive_Autovacuum parameter that & # x27 ; ll need to do is rebuild the index and it 's corrupted... In render of the structure of relations, caution is the best time use! Is no lock it implies that either the index to fix the problem to band aid it in Postgres! The correctness of the tables on which the job was running, skipping remaining... Post to the relation-level locks acquired when heapallindexed verification is supported have no whether... Composition guidelines beneficial to a missing filethat is postgres check if index is corrupted straightforward, of course 15 2023... And difficult to diagnose and fix this fundamentally and not try to band aid it your. Amcheck should ever be a false sense of confidence relying on their schedule! To know if there are missing records is a sample of the:! Also create a whole new copy of your data and your peace of mind bt_index_parent_check both output log about... Locks all writes of the indexs parent table up with references or personal experience rebuild... Being updated correctly that there is am extension called amcheck see Section38.16.3 for details operator! And post to the first segment 's file name is the same data was...