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Followup Re: Postgres locking: msg#00561

Subject: Followup Re: Postgres locking

OK, it looks like my problem was just the postgres server having a bad day, I just looked in the logfile and found this right after the LockAcquire errors:

DEBUG: all server processes terminated; reinitializing shared memory and semaphores
DEBUG:  database system was interrupted at 2003-02-25 16:32:14 PST
DEBUG:  checkpoint record is at 10/10C3F26C
DEBUG: redo record is at 10/10C3F26C; undo record is at 0/0; shutdown FALSE
DEBUG:  next transaction id: 686501; next oid: 85358132
DEBUG: database system was not properly shut down; automatic recovery in progress
DEBUG:  ReadRecord: record with zero length at 10/10C3F2AC
DEBUG:  redo is not required
FATAL 1:  The database system is starting up
DEBUG:  database system is ready

and now I can't get the LockAcquire errors to happen again at all. Looks like it was just a passing gremlin, hopefully it won't come back to visit too often.

Sorry for the noise on the list!

Bob

Begin forwarded message:

From: Bob Smith <bsmith@xxxxxxx>
Date: Tue Feb 25, 2003  16:55:57 US/Pacific
To: pgsql-sql <pgsql-sql@xxxxxxxxxxxxxx>
Subject: Postgres locking


I'm trying to use select for update locks in Postgres.  When I do this:

  begin work;
  select data from table where key = 1 for update;

in two psql's running simultaneously, about half the time the second transaction blocks and waits for the first to end (which is what I want it to do), the other half the time I get this:

  ERROR:  XactLockTableWait: LockAcquire failed

and the transaction is aborted. I can't find any pattern, if I do the same statements in the same order several times, it will be block one time and error the next apparently at random. I also tried using LOCK TABLE and found the same basic problem, sometimes the second transaction will block, other times it will abort with:

  ERROR:  LockRelation: LockAcquire failed

Do I have a configuration problem? Is this a bug in Postgres? I'm still running 7.2.1, would upgrading to 7.3 fix this?

Thanks!

Bob Smith
Hammett & Edison, Inc.
bsmith@xxxxxxx




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