Re: Nooby Q: Should this take five hours? And counting?

[Martin Gainty <mgainty@xxxxxxxxxxx>]

MG>take a look at the man page for vmstat

Martin Gainty
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> Date: Sat, 18 Apr 2009 18:55:59 -0600
> Subject: Re: Nooby Q: Should this take five hours? And counting?
> From: scott.marlowe@xxxxxxxxx
> To: kentilton@xxxxxxxxx
> CC: pgsql-general@xxxxxxxxxxxxxx
>
> On Sat, Apr 18, 2009 at 6:32 PM, Kenneth Tilton <kentilton@xxxxxxxxx> wrote:
> >
> >
> > Scott Marlowe wrote:
> >> On Sat, Apr 18, 2009 at 4:11 PM, Kenneth Tilton <kentilton@xxxxxxxxx>
> >> wrote:
> >>> ie, 5hrs and counting, no clue how long it intends to run, but methinks
> >>> this
> >>> is insane even if it is 10^7 records, mebbe half a dozen dups per value
> >>> (a
> >>> product-id usually around 8-chars long):
> >>>
> >>> CREATE INDEX web_source_items_by_item_id_strip
> >>>               ON web_source_items
> >>>               USING btree (item_id_strip);
> >>>
> >>> Am I unreasonably impatient?
> >>>
> >>> I see pg getting just a few % CPU on a heavily ram/core-endowed Sun box
> >>> with
> >>> nothing else going on. Mebbe they installed pg on a compact flash?
> >>> DVD-RW?
> >>> /usr/local/something, prolly not.
> >>
> >> What does vmstat 1 60 say during the index build?  Specifically the
> >> cpu columns for user, system, wa?
> >
> > uh-oh, Unix noob too, and unfortunately someone has jumped on with a
> > CPU-intensive task pegging one of the cores at 100%, so these numbers prolly
> > do not help, but here goes:
> >
> > procs -----------memory---------- ---swap-- -----io---- --system--
> > -----cpu------

FIELD DESCRIPTION FOR VM MODE

   Procs
       r: The number of processes waiting for run time.
       b: The number of processes in uninterruptible sleep.


   Memory
       swpd: the amount of virtual memory used.
       free: the amount of idle memory.
       buff: the amount of memory used as buffers.
       cache: the amount of memory used as cache.
       inact: the amount of inactive memory. (-a option)
       active: the amount of active memory. (-a option)


   Swap
       si: Amount of memory swapped in from disk (/s).
       so: Amount of memory swapped to disk (/s).


   IO
       bi: Blocks received from a block device (blocks/s).
       bo: Blocks sent to a block device (blocks/s).


   System
       in: The number of interrupts per second, including the clock.
       cs: The number of context switches per second.

   CPU
       These are percentages of total CPU time.
       us: Time spent running non-kernel code. (user time, including nice time)
       sy: Time spent running kernel code. (system time)
       id: Time spent idle. Prior to Linux 2.5.41, this includes IO-wait time.
       wa: Time spent waiting for IO. Prior to Linux 2.5.41, shown as zero.

> >  r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id
> > wa st
> >  1  1 2076312 1503204 182152 30669308   49   69   260   299    3    3 28  2
> > 63  7  0
> >  1  1 2076312 1502900 182152 30669656    0    0   192  2260 1198  332 25  1
> > 50 24  0
> >  1  1 2076312 1503024 182152 30669656    0    0     0   704 1181  282 25  1
> > 50 25  0
> >  1  3 2076312 1502904 182156 30669740    0    0   104  2780 1224  422 25  0
> > 48 26  0
> >  1  3 2076312 1502896 182156 30669740    0    0     0  1552 1173  309 25  0
> >
> > I'll sample again if I get a window, but these jobs tend to run for hours.
>
> I'm gonna take a guess about a few things:
> 1: You've got a lot of memory in that machine, try cranking up
> work_mem for this query to see if that helps
> 2: You've got a slow disk subsystem, if you're already seeing 25%
> IOWait with only ~2 to 3 megs a second being written.
>
> While having enough memory for everything to fit in it makes for fast
> reads, it doesn't do a lot to help with writes.
>
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