Re: GIN improvements part 1: additional information

On Wed, Jan 15, 2014 at 5:17 AM, Tomas Vondra <tv(at)fuzzy(dot)cz> wrote:

> On 14.1.2014 00:38, Tomas Vondra wrote:
> > On 13.1.2014 18:07, Alexander Korotkov wrote:
> >> On Sat, Jan 11, 2014 at 6:15 AM, Tomas Vondra <tv(at)fuzzy(dot)cz
> >> <mailto:tv(at)fuzzy(dot)cz>> wrote:
> >>
> >> On 8.1.2014 22:58, Alexander Korotkov wrote:
> >> > Thanks for reporting. Fixed version is attached.
> >>
> >> I've tried to rerun the 'archie' benchmark with the current patch,
> and
> >> once again I got
> >>
> >> PANIC: could not split GIN page, didn't fit
> >>
> >> I reran it with '--enable-cassert' and with that I got
> >>
> >> TRAP: FailedAssertion("!(ginCompareItemPointers(&items[i - 1],
> >> &items[i]) < 0)", File: "gindatapage.c", Line:
> 149)
> >> LOG: server process (PID 5364) was terminated by signal 6: Aborted
> >> DETAIL: Failed process was running: INSERT INTO messages ...
> >>
> >> so the assert in GinDataLeafPageGetUncompressed fails for some
> reason.
> >>
> >> I can easily reproduce it, but my knowledge in this area is rather
> >> limited so I'm not entirely sure what to look for.
> >>
> >>
> >> I've fixed this bug and many other bug. Now patch passes test suite that
> >> I've used earlier. The results are so:
> >
> > OK, it seems the bug is gone. However now there's a memory leak
> > somewhere. I'm loading pgsql mailing list archives (~600k messages)
> > using this script
> >
> > https://bitbucket.org/tvondra/archie/src/1bbeb920/bin/load.py
> >
> > And after loading about 1/5 of the data, all the memory gets filled by
> > the pgsql backends (loading the data in parallel) and the DB gets killed
> > by the OOM killer.
>
> I've spent a fair amount of time trying to locate the memory leak, but
> so far no luck. I'm not sufficiently familiar with the GIN code.
>
> I can however demonstrate that it's there, and I have rather simple test
> case to reproduce it - basically just a CREATE INDEX on a table with ~1M
> email message bodies (in a tsvector column). The data is available here
> (360MB compressed, 1GB raw):
>
> http://www.fuzzy.cz/tmp/message-b.data.gz
>
> Simply create a single-column table, load data and create the index
>
> CREATE TABLE test ( body_tsvector TSVECTOR );
> COPY test FROM '/tmp/message-b.data';
> CREATE test_idx ON test USING gin test ( body_tsvector );
>
> I'm running this on a machine with 8GB of RAM, with these settings
>
> shared_buffers=1GB
> maintenance_work_mem=1GB
>
> According to top, CREATE INDEX from the current HEAD never consumes more
> than ~25% of RAM:
>
> PID USER PR NI VIRT RES SHR %CPU %MEM COMMAND
> 32091 tomas 20 0 2026032 1,817g 1,040g 56,2 23,8 postgres
>
> which is about right, as (shared_buffers + maintenance_work_mem) is
> about 1/4 of RAM.
>
> With the v5 patch version applied, the CREATE INDEX process eventually
> goes crazy and allocates almost all the available memory (but somesimes
> finishes, mostly by pure luck). This is what I was able to get from top
>
> PID USER PR NI VIRT RES SHR S %CPU %MEM COMMAND
> 14090 tomas 20 0 7913820 6,962g 955036 D 4,3 91,1 postgres
>
> while the system was still reasonably responsive.
>

Thanks a lot for your help! I believe problem is that each decompressed
item pointers array is palloc'd but not freed. I hope to fix it today.

------
With best regards,
Alexander Korotkov.