Re: GiST indexes and concurrency (tsearch2)

Marinos,

what if you construct "apachebench & Co" free script and see if
the issue still exists. There are could be many issues doesn't
connected to postgresql and tsearch2.

Oleg

On Thu, 3 Feb 2005, Marinos J. Yannikos wrote:

> Oleg Bartunov wrote:
>> On Thu, 3 Feb 2005, Marinos J. Yannikos wrote:
>>> concurrent access to GiST indexes isn't possible at the moment. I [...]
>>
>> there are should no problem with READ access.
>
> OK, thanks everyone (perhaps it would make sense to clarify this in the
> manual).
>
>> I'm willing to see some details: version, query, explain analyze.
>
> 8.0.0
>
> Query while the box is idle:
>
> explain analyze select count(*) from fr_offer o, fr_merchant m where idxfti
> @@ to_tsquery('ranz & mc') and eur >= 70 and m.m_id=o.m_id;
>
> Aggregate (cost=2197.48..2197.48 rows=1 width=0) (actual time=88.052..88.054
> rows=1 loops=1)
> -> Merge Join (cost=2157.42..2196.32 rows=461 width=0) (actual
> time=88.012..88.033 rows=3 loops=1)
> Merge Cond: ("outer".m_id = "inner".m_id)
> -> Index Scan using fr_merchant_pkey on fr_merchant m
> (cost=0.00..29.97 rows=810 width=4) (actual time=0.041..1.233 rows=523
> loops=1)
> -> Sort (cost=2157.42..2158.57 rows=461 width=4) (actual
> time=85.779..85.783 rows=3 loops=1)
> Sort Key: o.m_id
> -> Index Scan using idxfti_idx on fr_offer o
> (cost=0.00..2137.02 rows=461 width=4) (actual time=77.957..85.754 rows=3
> loops=1)
> Index Cond: (idxfti @@ '\'ranz\' & \'mc\''::tsquery)
> Filter: (eur >= 70::double precision)
>
> Total runtime: 88.131 ms
>
> now, while using apachebench (-c10), "top" says this:
>
> Cpu0 : 15.3% us, 10.0% sy, 0.0% ni, 74.7% id, 0.0% wa, 0.0% hi, 0.0% si
> Cpu1 : 13.3% us, 11.6% sy, 0.0% ni, 75.1% id, 0.0% wa, 0.0% hi, 0.0% si
> Cpu2 : 16.9% us, 9.6% sy, 0.0% ni, 73.4% id, 0.0% wa, 0.0% hi, 0.0% si
> Cpu3 : 18.7% us, 14.0% sy, 0.0% ni, 67.0% id, 0.0% wa, 0.0% hi, 0.3% si
>
> (this is with shared_buffers = 2000; a larger setting makes almost no
> difference for overall performance: although according to "top" system time
> goes to ~0 and user time to ~25%, the system still stays 70-75% idle)
>
> vmstat:
>
> r b swpd free buff cache si so bi bo in cs us sy id
> wa
> 2 0 0 8654316 64908 4177136 0 0 56 35 279 286 5 1 94
> 0
> 2 0 0 8646188 64908 4177136 0 0 0 0 1156 2982 15 10 75
> 0
> 2 0 0 8658412 64908 4177136 0 0 0 0 1358 3098 19 11 70
> 0
> 1 0 0 8646508 64908 4177136 0 0 0 104 1145 2070 13 12 75
> 0
>
> so the script's execution speed is apparently not limited by the CPUs.
>
> The query execution times go up like this while apachebench is running (and
> the system is 75% idle):
>
> Aggregate (cost=2197.48..2197.48 rows=1 width=0) (actual
> time=952.661..952.663 rows=1 loops=1)
> -> Merge Join (cost=2157.42..2196.32 rows=461 width=0) (actual
> time=952.621..952.641 rows=3 loops=1)
> Merge Cond: ("outer".m_id = "inner".m_id)
> -> Index Scan using fr_merchant_pkey on fr_merchant m
> (cost=0.00..29.97 rows=810 width=4) (actual time=2.078..3.338 rows=523
> loops=1)
> -> Sort (cost=2157.42..2158.57 rows=461 width=4) (actual
> time=948.345..948.348 rows=3 loops=1)
> Sort Key: o.m_id
> -> Index Scan using idxfti_idx on fr_offer o
> (cost=0.00..2137.02 rows=461 width=4) (actual time=875.643..948.301 rows=3
> loops=1)
> Index Cond: (idxfti @@ '\'ranz\' & \'mc\''::tsquery)
> Filter: (eur >= 70::double precision)
> Total runtime: 952.764 ms
>
> I can't seem to find out where the bottleneck is, but it doesn't seem to be
> CPU or disk. "top" shows that postgres processes are frequently in this
> state:
>
> PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ WCHAN COMMAND
> 6701 postgres 16 0 204m 58m 56m S 9.3 0.2 0:06.96 semtimedo
> ^^^^^^^^^
> postmaste
>
> Any hints are appreciated...
>
> Regards,
> Marinos
>

Regards,
Oleg
_____________________________________________________________
Oleg Bartunov, sci.researcher, hostmaster of AstroNet,
Sternberg Astronomical Institute, Moscow University (Russia)
Internet: oleg(at)sai(dot)msu(dot)su, http://www.sai.msu.su/~megera/
phone: +007(095)939-16-83, +007(095)939-23-83