Re: Poor performance on seq scan - Mailing list pgsql-performance

From Tom Lane
Subject Re: Poor performance on seq scan
Date
Msg-id 17034.1158079926@sss.pgh.pa.us
Whole thread Raw
In response to Poor performance on seq scan  (Laszlo Nagy <gandalf@designaproduct.biz>)
Responses Re: Poor performance on seq scan
Re: Poor performance on seq scan
List pgsql-performance
Laszlo Nagy <gandalf@designaproduct.biz> writes:
> Meanwhile, "iostat 5" gives something like this:

>  tin tout  KB/t tps  MB/s   KB/t   tps  MB/s  us ni sy in id
>    1   14 128.00   1  0.10  128.00   1  0.10   5  0 94  1  0
>    0   12 123.98 104 12.56  123.74 104 12.56   8  0 90  2  0
>    0   12 125.66 128 15.75  125.26 128 15.68  10  0 85  6  0
>    0   12 124.66 129 15.67  124.39 129 15.64  12  0 85  3  0
>    0   12 117.13 121 13.87  117.95 121 13.96  12  0 84  5  0
>    0   12 104.84 118 12.05  105.84 118 12.19  10  0 87  2  0

Why is that showing 85+ percent *system* CPU time??  I could believe a
lot of idle CPU if the query is I/O bound, or a lot of user time if PG
was being a hog about doing the ~~ comparisons (not too unlikely BTW).
But if the kernel is eating all the CPU, there's something very wrong,
and I don't think it's Postgres' fault.

            regards, tom lane

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