Concurrent update failure in HEAD
I found pgbench sometimes receives responces of "UPDATE 0" from HEAD server.
When I re-tested pgbench with 8.4.2 server, all of the results were "UPDATE 1".
Are there known issues in HEAD for concurrent updates?
There were no problems if I used a few (1 or 2) connections, but 3 or more
connections returns 0-UPDATEs. Since it also failed with -j1, multi-threading
has nothing to do with the issue. So, there might be a bug in the server.
I wrote the attached just for debugging. Strangely, even if it returns
"UPDATE 0", I can retrive a row with the same condition after pgbench.
$ pgbench -i
$ pgbench -c3 -j1 -T10
starting vacuum...end.
[0]: variable: tid = 1
[0]: variable: tid = 1
[0]: variable: tid = 1
[0]: variable: tid = 1
[0]: variable: tid = 1
[0]: variable: tid = 1
[0]: variable: tid = 1
[0]: variable: tid = 1
[0]: variable: tid = 1
$ psql -c "SELECT * FROM pgbench_branches WHERE bid = 1;"
bid | bbalance | filler
-----+----------+--------
1 | -27026 |
(1 row)
I found the issue when I tested pg_stat_statements with pgbench.
There were differences in 'calls' and 'rows' fields in it, but
it should be same because pgbench always updates a row per query.
Regards,
---
Takahiro Itagaki
NTT Open Source Software Center
Attachments:
pgbench_debug.patchapplication/octet-stream; name=pgbench_debug.patchDownload+20-0
Takahiro Itagaki <itagaki.takahiro@oss.ntt.co.jp> writes:
I found pgbench sometimes receives responces of "UPDATE 0" from HEAD server.
When I re-tested pgbench with 8.4.2 server, all of the results were "UPDATE 1".
Are there known issues in HEAD for concurrent updates?
I suspect it might have something to do with the recent EvalPlanQual
rewrite, but exactly what the problem is is not clear.
regards, tom lane
Takahiro Itagaki <itagaki.takahiro@oss.ntt.co.jp> writes:
I found pgbench sometimes receives responces of "UPDATE 0" from HEAD server.
When I re-tested pgbench with 8.4.2 server, all of the results were "UPDATE 1".
Are there known issues in HEAD for concurrent updates?
There are now :-(. I've committed a fix that I think takes care of
this, but since it seems to be a quite hard-to-reach path of control,
please test some more.
regards, tom lane
Tom Lane <tgl@sss.pgh.pa.us> wrote:
Takahiro Itagaki <itagaki.takahiro@oss.ntt.co.jp> writes:
I found pgbench sometimes receives responces of "UPDATE 0" from HEAD server.
When I re-tested pgbench with 8.4.2 server, all of the results were "UPDATE 1".
Are there known issues in HEAD for concurrent updates?There are now :-(. I've committed a fix that I think takes care of
this, but since it seems to be a quite hard-to-reach path of control,
please test some more.
Excellent! It worked perfenct and I don't see update failure anymore.
I hope we will have additional regression tests to find such kind of bugs.
Regards,
---
Takahiro Itagaki
NTT Open Source Software Center