Re: Calculation of a shared memory

Hi.

From: "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us>

> "Hiroshi Saito" <z-saito(at)guitar(dot)ocn(dot)ne(dot)jp> writes:
>> inet% ipcs -b -m
>> Shared Memory:
>> T ID KEY MODE OWNER GROUP SEGSZ
>> m 917504 5432001 --rw------- saito wheel 32571392
>
>> 40*(400+270*64)= 707200
>> 5*(600+270*64)= 89400
>> 28MB= 29360128
>> 64kB= 65536
>> 1000*70= 70000
>> 179200*6= 1075200
>
>> Total :31367464
>> ipcs-m:32571392
>> -1203928 (difference is large: why?)
>
> Hmm, those numbers never got updated for 8.2. The per-backend
> multiplier is particularly off, since it's not accounting for
> the in-memory pg_stat_activity array (PgBackendStatus is 1208
> bytes on my machine...) Also, you neglected to add the fixed space,
> which was claimed to be 500K as of 8.1, but seems to have bloated
> to about 700K in 8.2 and 770K in HEAD.

Sent: Friday, November 02, 2007 4:11 AM
Subject: [COMMITTERS] pgsql: Update shared-memory-size info for 8.2 branch.

Great, taken into consideration.

40*(1800+270*64)= 763200
5*(700+270*64)= 89900
28MB=29360128
64kB= 65536
1000*70= 70000
179200*6= 1075200
700kB= 716800

Total :32140764
ipcs-m:32571392
-430628

I think it is a permissible range. Thanks!

Regards,
Hiroshi Saito