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@sai.msu.su, http://www.sai.msu.su/~megera/
phone: +007(095)939-16-83, +007(095)939-23-83