Hi, On Thu, Dec 15, 2016 at 12:07:54AM -0800, Alex Vandiver wrote: >... > However, upon writing this, it occurs to me that Postgres' default > isolation level is _also_ "read committed."[4] Thus any possible race > conditions that might show up under NDB are also possible under > Postgres. I'd need to do some close analysis to determine if this > means that Postgres is open to data corruption, or if both are safe > because the queries RT runs do not care about repeatable-read > semantics. >...
I afraid you are right, Postgreses default isolation level is 'read committed'. I filled bug-report two months ago. https://issues.bestpractical.com/Ticket/Display.html?id=32381 I'm running PostgreSQL & RT on Debian Jessie, that is Pg 9.4 & RT 4.4.1. I did only a basic PostgreSQL performance tuning, but didn't change the default transaction isolation level. I can't find anything about needed transaction isolation level through RT documentation. I read this fact, that RT assumes "repeatable-read" isolation level for the first time. Nevertheless we are hit only by the problem during Comment/Correspond together with ticket owner change only (I hope). I did some testing right now on testing RT instance: ================================================================ * default "committed read" isolation level - I'm getting from time to time: 2016-12-21 11:33:38 CET [22545-1] rt_rt@rt ERROR: deadlock detected 2016-12-21 11:33:38 CET [22545-2] rt_rt@rt DETAIL: Process 22545 waits for ShareLock on transaction 8351856; blocked by process 22539. Process 22539 waits for ShareLock on transaction 8351857; blocked by process 22545. Process 22545: UPDATE Tickets SET Owner=$1 WHERE id=$2 Process 22539: INSERT INTO GroupMembers (LastUpdatedBy, LastUpdated, GroupId, MemberId, Creator, Created) VALUES ($1, $2, $3, $4, $5, $6) 2016-12-21 11:33:38 CET [22545-3] rt_rt@rt HINT: See server log for query details. 2016-12-21 11:33:38 CET [22545-4] rt_rt@rt CONTEXT: while updating tuple (4336,144) in relation "tickets" 2016-12-21 11:33:38 CET [22545-5] rt_rt@rt STATEMENT: UPDATE Tickets SET Owner=$1 WHERE id=$2 ================================================================ * default_transaction_isolation = 'repeatable read' - I'm getting the following errors, but on the application level things seems to be normal. 2016-12-21 17:20:41 CET [25923-1] rt_rt@rt ERROR: could not serialize access due to concurrent update 2016-12-21 17:20:41 CET [25923-2] rt_rt@rt STATEMENT: SELECT * FROM Tickets WHERE id = $1 FOR UPDATE 2016-12-21 17:20:41 CET [25923-3] rt_rt@rt ERROR: current transaction is aborted, commands ignored until end of transaction block 2016-12-21 17:20:41 CET [25923-4] rt_rt@rt STATEMENT: INSERT INTO Transactions (OldReference, ObjectType, Data, Field, ObjectId, Type, NewValue, ReferenceType, OldValue, Created, NewReference, Creator) VALUES ($1, $2, $3, $4, $5, $6, $7, $8, $9, $10, $11, $12) 2016-12-21 17:20:41 CET [25923-5] rt_rt@rt ERROR: current transaction is aborted, commands ignored until end of transaction block 2016-12-21 17:20:41 CET [25923-6] rt_rt@rt STATEMENT: SELECT * FROM Transactions WHERE id = $1 2016-12-21 17:20:41 CET [25923-7] rt_rt@rt ERROR: current transaction is aborted, commands ignored until end of transaction block 2016-12-21 17:20:41 CET [25923-8] rt_rt@rt STATEMENT: SELECT * FROM Tickets WHERE id = $1 2016-12-21 17:20:41 CET [25923-9] rt_rt@rt ERROR: current transaction is aborted, commands ignored until end of transaction block 2016-12-21 17:20:41 CET [25923-10] rt_rt@rt STATEMENT: SELECT * FROM Transactions WHERE id = $1 2016-12-21 17:20:41 CET [25923-11] rt_rt@rt ERROR: current transaction is aborted, commands ignored until end of transaction block 2016-12-21 17:20:41 CET [25923-12] rt_rt@rt STATEMENT: SELECT main.* FROM Scrips main JOIN ObjectScrips ObjectScrips_1 ON ( ObjectScrips_1.Scrip = main.id ) JOIN ScripConditions ScripConditions_2 ON ( ScripConditions_2.id = main.ScripCondition ) WHERE (ObjectScrips_1.ObjectId = '0') AND (ObjectScrips_1.Stage = 'TransactionCreate') AND (ScripConditions_2.ApplicableTransTypes LIKE '%Comment%' OR ScripConditions_2.ApplicableTransTypes LIKE '%Any%') AND (main.Disabled = '0') GROUP BY main.id ORDER BY MIN(ObjectScrips_1.SortOrder) ASC 2016-12-21 17:20:41 CET [25923-13] rt_rt@rt ERROR: current transaction is aborted, commands ignored until end of transaction block 2016-12-21 17:20:41 CET [25923-14] rt_rt@rt STATEMENT: SELECT COUNT(DISTINCT main.id) FROM Scrips main JOIN ObjectScrips ObjectScrips_1 ON ( ObjectScrips_1.Scrip = main.id ) JOIN ScripConditions ScripConditions_2 ON ( ScripConditions_2.id = main.ScripCondition ) WHERE (ObjectScrips_1.ObjectId = '0') AND (ObjectScrips_1.Stage = 'TransactionCreate') AND (ScripConditions_2.ApplicableTransTypes LIKE '%Comment%' OR ScripConditions_2.ApplicableTransTypes LIKE '%Any%') AND (main.Disabled = '0') 2016-12-21 17:20:41 CET [25923-15] rt_rt@rt ERROR: current transaction is aborted, commands ignored until end of transaction block 2016-12-21 17:20:41 CET [25923-16] rt_rt@rt STATEMENT: SELECT main.* FROM Scrips main JOIN ObjectScrips ObjectScrips_1 ON ( ObjectScrips_1.Scrip = main.id ) JOIN ScripConditions ScripConditions_2 ON ( ScripConditions_2.id = main.ScripCondition ) WHERE (ObjectScrips_1.ObjectId = '0') AND (ObjectScrips_1.Stage = 'TransactionCreate') AND (ScripConditions_2.ApplicableTransTypes LIKE '%Comment%' OR ScripConditions_2.ApplicableTransTypes LIKE '%Any%') AND (main.Disabled = '0') GROUP BY main.id ORDER BY MIN(ObjectScrips_1.SortOrder) ASC 2016-12-21 17:20:41 CET [25923-17] rt_rt@rt ERROR: current transaction is aborted, commands ignored until end of transaction block 2016-12-21 17:20:41 CET [25923-18] rt_rt@rt STATEMENT: SELECT * FROM Tickets WHERE id = $1 2016-12-21 17:20:41 CET [25923-19] rt_rt@rt ERROR: current transaction is aborted, commands ignored until end of transaction block 2016-12-21 17:20:41 CET [25923-20] rt_rt@rt STATEMENT: SELECT * FROM Transactions WHERE id = $1 2016-12-21 17:20:41 CET [25923-21] rt_rt@rt ERROR: current transaction is aborted, commands ignored until end of transaction block 2016-12-21 17:20:41 CET [25923-22] rt_rt@rt STATEMENT: SELECT * FROM Tickets WHERE id = $1 2016-12-21 17:20:41 CET [25923-23] rt_rt@rt ERROR: current transaction is aborted, commands ignored until end of transaction block 2016-12-21 17:20:41 CET [25923-24] rt_rt@rt STATEMENT: UPDATE Tickets SET LastUpdated=$1 WHERE id=$2 2016-12-21 17:20:41 CET [25923-25] rt_rt@rt ERROR: current transaction is aborted, commands ignored until end of transaction block 2016-12-21 17:20:41 CET [25923-26] rt_rt@rt STATEMENT: UPDATE Tickets SET LastUpdated=$1 WHERE id=$2 2016-12-21 17:20:41 CET [25923-27] rt_rt@rt ERROR: current transaction is aborted, commands ignored until end of transaction block 2016-12-21 17:20:41 CET [25923-28] rt_rt@rt STATEMENT: UPDATE Tickets SET LastUpdated=$1 WHERE id=$2 2016-12-21 17:20:41 CET [25923-29] rt_rt@rt ERROR: current transaction is aborted, commands ignored until end of transaction block 2016-12-21 17:20:41 CET [25923-30] rt_rt@rt STATEMENT: SELECT * FROM Tickets WHERE id = $1 2016-12-21 17:20:41 CET [25923-31] rt_rt@rt ERROR: current transaction is aborted, commands ignored until end of transaction block 2016-12-21 17:20:41 CET [25923-32] rt_rt@rt STATEMENT: SELECT * FROM Users WHERE id = $1 2016-12-21 17:20:41 CET [25923-33] rt_rt@rt ERROR: current transaction is aborted, commands ignored until end of transaction block 2016-12-21 17:20:41 CET [25923-34] rt_rt@rt STATEMENT: SELECT * FROM Users WHERE id = $1 2016-12-21 17:20:41 CET [25923-35] rt_rt@rt ERROR: current transaction is aborted, commands ignored until end of transaction block 2016-12-21 17:20:41 CET [25923-36] rt_rt@rt STATEMENT: SELECT * FROM Users WHERE id = $1 ================================================================ * default_transaction_isolation = 'serializable' - I tried the action many times, but Pg is silent - nothing appears in its log file and everything seems normal. Is there somebody with RT 4.4.1 (versions 4.2.x not suffers by this) and PostgreSQL with similar symptoms? The problem occurs probably only when we did action Comment or Correspond and change the ticket owner in the one transaction. Is it safe for me to change the default_transaction_isolation in /etc/postgresql/9.4/main/postgresql.conf to 'repeatable read' ? I'm a bit confused by errors above, maybe the failed transaction was restarted? Regards -- Zito
