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* Default shared memory SGML mention
@ 2001-05-02 16:17 Bruce Momjian <pgman@candle.pha.pa.us>
0 siblings, 1 reply; 10+ messages in thread
From: Bruce Momjian @ 2001-05-02 16:17 UTC (permalink / raw)
To: pgsql-docs
I am looking over the shared memory SGML files, and found that on my
BSD/OS system, I get as the following default shared memory size:
m 131072 5432001 --rw------- postgres user postgres
user 1 1236992 10622 10622 12:11:14 12:11:15 12:11:14
^^^^^^^
I have highlighted the size. If I subtract the default shared memory
buffers, I get:
1236992 - 8192 * 64
712704
so by my computations, we need about 700k added to the shared buffer
cache area. The documentation says to add 512k, not 700k. My guess is
that the non-cached shared memory area has increased in a recent
release, and docs were not updated. I will bump up the SGML mention to
700k unless someone shows a lower default shared memory size.
--
Bruce Momjian | http://candle.pha.pa.us
pgman@candle.pha.pa.us | (610) 853-3000
+ If your life is a hard drive, | 830 Blythe Avenue
+ Christ can be your backup. | Drexel Hill, Pennsylvania 19026
^ permalink raw reply [nested|flat] 10+ messages in thread
* Re: Default shared memory SGML mention
@ 2001-05-02 22:08 Tom Lane <tgl@sss.pgh.pa.us>
parent: Bruce Momjian <pgman@candle.pha.pa.us>
0 siblings, 1 reply; 10+ messages in thread
From: Tom Lane @ 2001-05-02 22:08 UTC (permalink / raw)
To: Bruce Momjian <pgman@candle.pha.pa.us>; +Cc: pgsql-docs
Bruce Momjian <pgman@candle.pha.pa.us> writes:
> so by my computations, we need about 700k added to the shared buffer
> cache area. The documentation says to add 512k, not 700k.
This would depend on your -N setting.
A little experimentation shows that the present multiplier for -B is
about 8350 bytes and the multiplier for -N about 14580 bytes on my
system (HPUX), which extrapolates to a fixed base of about 250K plus
the -B and -N contributions. In reality I believe the computation
is somewhat nonlinear, but that's probably close enough for starters.
regards, tom lane
^ permalink raw reply [nested|flat] 10+ messages in thread
* Re: Default shared memory SGML mention
@ 2001-05-08 18:01 Bruce Momjian <pgman@candle.pha.pa.us>
parent: Tom Lane <tgl@sss.pgh.pa.us>
0 siblings, 1 reply; 10+ messages in thread
From: Bruce Momjian @ 2001-05-08 18:01 UTC (permalink / raw)
To: Tom Lane <tgl@sss.pgh.pa.us>; +Cc: pgsql-docs
> Bruce Momjian <pgman@candle.pha.pa.us> writes:
> > so by my computations, we need about 700k added to the shared buffer
> > cache area. The documentation says to add 512k, not 700k.
>
> This would depend on your -N setting.
>
> A little experimentation shows that the present multiplier for -B is
> about 8350 bytes and the multiplier for -N about 14580 bytes on my
> system (HPUX), which extrapolates to a fixed base of about 250K plus
> the -B and -N contributions. In reality I believe the computation
> is somewhat nonlinear, but that's probably close enough for starters.
I have updated the SGML sources to say for default shared memory values:
250 kB + 8192 * buffers or infinity
Of course, buffers is 2 * connections by default.
--
Bruce Momjian | http://candle.pha.pa.us
pgman@candle.pha.pa.us | (610) 853-3000
+ If your life is a hard drive, | 830 Blythe Avenue
+ Christ can be your backup. | Drexel Hill, Pennsylvania 19026
^ permalink raw reply [nested|flat] 10+ messages in thread
* Re: Default shared memory SGML mention
@ 2001-05-08 20:05 Tom Lane <tgl@sss.pgh.pa.us>
parent: Bruce Momjian <pgman@candle.pha.pa.us>
0 siblings, 1 reply; 10+ messages in thread
From: Tom Lane @ 2001-05-08 20:05 UTC (permalink / raw)
To: Bruce Momjian <pgman@candle.pha.pa.us>; +Cc: pgsql-docs
Bruce Momjian <pgman@candle.pha.pa.us> writes:
>> A little experimentation shows that the present multiplier for -B is
>> about 8350 bytes and the multiplier for -N about 14580 bytes on my
>> system (HPUX), which extrapolates to a fixed base of about 250K plus
>> the -B and -N contributions. In reality I believe the computation
>> is somewhat nonlinear, but that's probably close enough for starters.
> I have updated the SGML sources to say for default shared memory values:
> 250 kB + 8192 * buffers or infinity
How did infinity get into this? And what happened to the -N
contribution?
regards, tom lane
^ permalink raw reply [nested|flat] 10+ messages in thread
* Re: Default shared memory SGML mention
@ 2001-05-08 20:06 Bruce Momjian <pgman@candle.pha.pa.us>
parent: Tom Lane <tgl@sss.pgh.pa.us>
0 siblings, 1 reply; 10+ messages in thread
From: Bruce Momjian @ 2001-05-08 20:06 UTC (permalink / raw)
To: Tom Lane <tgl@sss.pgh.pa.us>; +Cc: pgsql-docs
> Bruce Momjian <pgman@candle.pha.pa.us> writes:
> >> A little experimentation shows that the present multiplier for -B is
> >> about 8350 bytes and the multiplier for -N about 14580 bytes on my
> >> system (HPUX), which extrapolates to a fixed base of about 250K plus
> >> the -B and -N contributions. In reality I believe the computation
> >> is somewhat nonlinear, but that's probably close enough for starters.
>
> > I have updated the SGML sources to say for default shared memory values:
>
> > 250 kB + 8192 * buffers or infinity
>
> How did infinity get into this? And what happened to the -N
> contribution?
Infinity was always there. The column is labeled "Typical Values". As
far as -N, buffers is always 2*N, right, so I figured it was in there
already.
--
Bruce Momjian | http://candle.pha.pa.us
pgman@candle.pha.pa.us | (610) 853-3000
+ If your life is a hard drive, | 830 Blythe Avenue
+ Christ can be your backup. | Drexel Hill, Pennsylvania 19026
^ permalink raw reply [nested|flat] 10+ messages in thread
* Re: Default shared memory SGML mention
@ 2001-05-08 20:17 Tom Lane <tgl@sss.pgh.pa.us>
parent: Bruce Momjian <pgman@candle.pha.pa.us>
0 siblings, 1 reply; 10+ messages in thread
From: Tom Lane @ 2001-05-08 20:17 UTC (permalink / raw)
To: Bruce Momjian <pgman@candle.pha.pa.us>; +Cc: pgsql-docs
Bruce Momjian <pgman@candle.pha.pa.us> writes:
> far as -N, buffers is always 2*N, right, so I figured it was in there
> already.
No, it isn't, and buffers is NOT always 2*N.
regards, tom lane
^ permalink raw reply [nested|flat] 10+ messages in thread
* Re: Default shared memory SGML mention
@ 2001-05-08 20:23 Bruce Momjian <pgman@candle.pha.pa.us>
parent: Tom Lane <tgl@sss.pgh.pa.us>
0 siblings, 1 reply; 10+ messages in thread
From: Bruce Momjian @ 2001-05-08 20:23 UTC (permalink / raw)
To: Tom Lane <tgl@sss.pgh.pa.us>; +Cc: pgsql-docs
> Bruce Momjian <pgman@candle.pha.pa.us> writes:
> > far as -N, buffers is always 2*N, right, so I figured it was in there
> > already.
>
> No, it isn't, and buffers is NOT always 2*N.
Yes, but shared memory limits are based on buffers, not connections,
right? The per-connection overhead is pretty small, no?
If it is buffers and connections, how much is connections and how much
buffers. I know buffers is 8k.
--
Bruce Momjian | http://candle.pha.pa.us
pgman@candle.pha.pa.us | (610) 853-3000
+ If your life is a hard drive, | 830 Blythe Avenue
+ Christ can be your backup. | Drexel Hill, Pennsylvania 19026
^ permalink raw reply [nested|flat] 10+ messages in thread
* Re: Default shared memory SGML mention
@ 2001-05-08 20:37 Tom Lane <tgl@sss.pgh.pa.us>
parent: Bruce Momjian <pgman@candle.pha.pa.us>
0 siblings, 2 replies; 10+ messages in thread
From: Tom Lane @ 2001-05-08 20:37 UTC (permalink / raw)
To: Bruce Momjian <pgman@candle.pha.pa.us>; +Cc: pgsql-docs
Bruce Momjian <pgman@candle.pha.pa.us> writes:
> Yes, but shared memory limits are based on buffers, not connections,
> right? The per-connection overhead is pretty small, no?
I gave you my experimentally-derived formula already:
250Kb + 8350 * B + 14580 * N
I don't see how you can consider the N term negligible.
regards, tom lane
^ permalink raw reply [nested|flat] 10+ messages in thread
* Re: Default shared memory SGML mention
@ 2001-05-08 20:54 Bruce Momjian <pgman@candle.pha.pa.us>
parent: Tom Lane <tgl@sss.pgh.pa.us>
1 sibling, 0 replies; 10+ messages in thread
From: Bruce Momjian @ 2001-05-08 20:54 UTC (permalink / raw)
To: Tom Lane <tgl@sss.pgh.pa.us>; +Cc: pgsql-docs
> Bruce Momjian <pgman@candle.pha.pa.us> writes:
> > Yes, but shared memory limits are based on buffers, not connections,
> > right? The per-connection overhead is pretty small, no?
>
> I gave you my experimentally-derived formula already:
>
> 250Kb + 8350 * B + 14580 * N
>
> I don't see how you can consider the N term negligible.
Oh, I misread it. I thought the 14.5k was part of the 250k. Let me fix
that.
--
Bruce Momjian | http://candle.pha.pa.us
pgman@candle.pha.pa.us | (610) 853-3000
+ If your life is a hard drive, | 830 Blythe Avenue
+ Christ can be your backup. | Drexel Hill, Pennsylvania 19026
^ permalink raw reply [nested|flat] 10+ messages in thread
* Re: Default shared memory SGML mention
@ 2001-05-08 21:11 Bruce Momjian <pgman@candle.pha.pa.us>
parent: Tom Lane <tgl@sss.pgh.pa.us>
1 sibling, 0 replies; 10+ messages in thread
From: Bruce Momjian @ 2001-05-08 21:11 UTC (permalink / raw)
To: Tom Lane <tgl@sss.pgh.pa.us>; +Cc: pgsql-docs
> Bruce Momjian <pgman@candle.pha.pa.us> writes:
> > Yes, but shared memory limits are based on buffers, not connections,
> > right? The per-connection overhead is pretty small, no?
>
> I gave you my experimentally-derived formula already:
>
> 250Kb + 8350 * B + 14580 * N
>
> I don't see how you can consider the N term negligible.
OK, patch applied.
--
Bruce Momjian | http://candle.pha.pa.us
pgman@candle.pha.pa.us | (610) 853-3000
+ If your life is a hard drive, | 830 Blythe Avenue
+ Christ can be your backup. | Drexel Hill, Pennsylvania 19026
Attachments:
/bjm/diff (text/plain, 831B) download
Index: doc/src/sgml/runtime.sgml
===================================================================
RCS file: /home/projects/pgsql/cvsroot/pgsql/doc/src/sgml/runtime.sgml,v
retrieving revision 1.64
diff -c -r1.64 runtime.sgml
*** doc/src/sgml/runtime.sgml 2001/05/07 15:55:27 1.64
--- doc/src/sgml/runtime.sgml 2001/05/08 21:09:21
***************
*** 1481,1487 ****
<row>
<entry><varname>SHMMAX</></>
<entry>Maximum size of shared memory segment (bytes)</>
! <entry>250 kB + 8192 * buffers or infinity</entry>
</row>
<row>
--- 1481,1487 ----
<row>
<entry><varname>SHMMAX</></>
<entry>Maximum size of shared memory segment (bytes)</>
! <entry>250 kB + 8.2kB * buffers + 14.2kB * max_connections or infinity</entry>
</row>
<row>
end of thread, other threads:[~2001-05-08 21:11 UTC | newest]
Thread overview: 10+ messages (download: mbox mbox.gz follow: Atom feed)
-- links below jump to the message on this page --
2001-05-02 16:17 Default shared memory SGML mention Bruce Momjian <pgman@candle.pha.pa.us>
2001-05-02 22:08 ` Tom Lane <tgl@sss.pgh.pa.us>
2001-05-08 18:01 ` Bruce Momjian <pgman@candle.pha.pa.us>
2001-05-08 20:05 ` Tom Lane <tgl@sss.pgh.pa.us>
2001-05-08 20:06 ` Bruce Momjian <pgman@candle.pha.pa.us>
2001-05-08 20:17 ` Tom Lane <tgl@sss.pgh.pa.us>
2001-05-08 20:23 ` Bruce Momjian <pgman@candle.pha.pa.us>
2001-05-08 20:37 ` Tom Lane <tgl@sss.pgh.pa.us>
2001-05-08 20:54 ` Bruce Momjian <pgman@candle.pha.pa.us>
2001-05-08 21:11 ` Bruce Momjian <pgman@candle.pha.pa.us>
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