Re: Calculation of a shared memory

"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.

regards, tom lane