The engine configurations also include several parameters that control the PostgreSQL logging behavior. DB parameter groupsĮach RDS and Aurora PostgreSQL instance is associated with a parameter group that contains the engine specific configurations. This post provides more details about enabling this logging and its benefits. This log information can help troubleshoot potential performance and auditing issues while using the database. These logging parameters help capture information such as connections and disconnections, schema modification queries, all slow queries with the duration, queries taking time because they are waiting for locks, queries consuming temporary disk storage, and the backend auto-vacuum process consuming resources. In addition to the default logging, you can modify PostgreSQL logging parameters to capture beneficial information in identifying and solving issues such as poor performance and security audits. These incorrectly formatted queries generate error messages in the logs, which can help identify the problematic application code. For example, if you converted a legacy application from Oracle to PostgreSQL, some queries may not convert correctly to PostgreSQL syntax. These error messages help identify various application issues. SQL query failures, failed login attempts, and deadlocks are captured in the database logs by default. PostgreSQL generates event logs that contain useful information for DBAs. The second part of this post, Working with RDS and Aurora PostgreSQL Logs: Part 2, shares methods to access these log files. This post discusses how you can configure RDS and Aurora PostgreSQL to generate additional engine logs. One of the common questions that new PostgreSQL users ask is how to capture the database activity logs for debugging and monitoring purposes. AWS provides two managed PostgreSQL options: Amazon RDS for PostgreSQL and Amazon Aurora PostgreSQL. With more than 30 years of development work, PostgreSQL has proven to be a highly reliable and robust database that can handle a large number of complicated data workloads. I hope this post will help someone debugging his Postgres deadlock - if it does, I did my good deed for the day.PostgreSQL is one of the most popular open-source relational database systems. Understanding the problem, though, will help you in choosing the right solution for your case. The solution for your cases might be different, and is rather application specific. Now, in our case the solution was just synchronizing the code block which updates the entities and causes the deadlock. The fact we are actually seeing a ShareLock on a transaction has to do with Postgres' deadlock detector, and the issue is explain here. (You can read more about the different locks Postgres uses here) This lock conflicts with the RowShareLock, and so each process waits for the second one to release the RowShareLock - thus the deadlock. When both processes come to the update statement, things become interesting. The insert from the second process also acquires a RowShareLock on the same row (acquiring two RowShareLocks is fine). The deadlock comes from the fact that when inserting a new row to the Child table, Postres acquires a RowShareLock on the Parent row (because of the foreign key). I would just expect one of the processes to fail when trying to update the Parent row. Running these two simultaneously would result in the error above.Īt first it seems a little weird that this scenario gives a deadlock. UPDATE "Parent" SET "Name"='Parent_C' WHERE "ID"=1 INSERT INTO "Child" VALUES (2, 1, 'CHILD_B') UPDATE "Parent" SET "Name"='Parent_B' WHERE "ID"=1 INSERT INTO "Child" VALUES (1, 1, 'CHILD_A') (Assume the Parent has columns: ID, Name, and the Child has columns: ID, Parent_ID, Name) After each insert we will also try to update the name of the parent. ![]() Given 2 tables, Parent and Child, we will try to add two children to the same parent from two different processes. These are usually hard to reproduce, and not simple to solve.Īfter reading a little about the different locks in Postgres and when they are used I came up with the following simple scenario which reproduces this error: Usually for me a deadlock error is a bad way to start the day. Process 4924 waits for ShareLock on transaction 689 blocked by process 552. Of database 12002 blocked by process 4924. This would look something like that:ĭETAIL: Process 552 waits for ExclusiveLock on tuple (0,3) of relation 16393 The general setting we are talking about is Java, Spring-Data, Hibernate, Postgres, though the main issue is the Postgres DB. What better way to do that than through a blog. It took me some time to figure out the exact situation that was causing this deadlock, and so I decided to share what I've learned. So I ran a few days ago into a pretty weird deadlock error in my logs.
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