I notice that if an ERROR occurs during ProcessCatchupEvent() then the messages back to client get out of sync with each other. I've inserted an optional error into ProcessCatchupEvent() to show what happens (attached).
> postgres=# begin; > BEGIN > postgres=# d; > ERROR: an error occurred while processing catchup event > postgres=# commit; > ERROR: syntax error at or near "d" > LINE 1: commit; > ^ > postgres=# commit; > ROLLBACK > postgres=# begin; > WARNING: there is no transaction in progress > COMMIT Notice how "commit" has been issued twice... and that there is no "d" in commit. LOL, but :-( This issue happens to be exactly the same as the one I have while trying to make SIGINT cancel an idle-in-transaction session. I was looking at the catchup interrupt to try to learn more about this area of code, only to find the same problem exists there also. Perhaps there is no possibility of an ERROR happening during catchup processing, but looking at the rest of ProcessCatchupEvent(), I doubt it. (The attached patch allows behaviour to be turned on/off using synchronous_commit but that has *nothing* to do with this issue and was chosen to avoid inventing a new switch based on what was in miscadmin.h) It looks to me that generating a single error message while idle causes the server to provide ErrorResponse, which the client assumes is the end of the processing of that statement as defined in FE/BE protocol. Yet server continues processing anyway and gives second response later. This also behaves differently on some tests, generating an infinite loop of messages to the log and on the psql client like this: ERROR: an error occurred while processing catchup event message type 0x5a arrived from server while idle ERROR: an error occurred while processing catchup event message type 0x5a arrived from server while idle ... having used over 8 minutes of CPU as I post this, with 1 CPU at 100%, even after the client disconnects. Thoughts, go-look-theres or other comments welcome. -- Simon Riggs www.2ndQuadrant.com PostgreSQL Training, Services and Support
Index: src/backend/storage/ipc/sinval.c =================================================================== RCS file: /home/sriggs/pg/REPOSITORY/pgsql/src/backend/storage/ipc/sinval.c,v retrieving revision 1.89 diff -c -r1.89 sinval.c *** src/backend/storage/ipc/sinval.c 1 Jan 2009 17:23:47 -0000 1.89 --- src/backend/storage/ipc/sinval.c 5 Jan 2009 19:03:45 -0000 *************** *** 303,308 **** --- 303,311 ---- /* Must prevent SIGUSR2 interrupt while I am running */ notify_enabled = DisableNotifyInterrupt(); + if (!XactSyncCommit) + elog(ERROR, "an error occurred while processing catchup event"); + /* * What we need to do here is cause ReceiveSharedInvalidMessages() to run, * which will do the necessary work and also reset the
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