Re: GiST indexes and concurrency (tsearch2)

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
--
Dipl.-Ing. Marinos Yannikos, CEO
Preisvergleich Internet Services AG
Obere Donaustraße 63/2, A-1020 Wien
Tel./Fax: (+431) 5811609-52/-55