Re: Shared memory usage in PostgreSQL 9.1

Am 03.12.2011 13:39, schrieb Christoph Zwerschke:
> According to that table the usage would be:
> Connections: 1908000 Bytes
> Autovac workers: 57240 Bytes
> Prepared transactions: 0 Bytes
> Shared disk buffers: 400MB
> WAL buffers: 16MB
> Fixed space: 788480 Bytes
> Sum: 435145336
>
> This is about 16MB less than what is really requested.

Just so that this summation does not stay uncorrected: The major
discrepancy accrued because my values for shared disk buffers and WAL
buffers were wrong. They must be calculated as

Shared disk buffers = (1 + 208/8192) * 400MB = 430080000 Bytes
WAL buffers = (1 + 8/8192) * 16MB = 16793600 Bytes

Then, the corrected sum is 449627320 Bytes, which is only about 2MB less
than was requested. This remaining discrepancy can probably be explained
by additional overhead for a PostgreSQL 9.1 64bit server vs. a
PostgreSQL 8.3 32bit server for which the table was valid.

-- Christoph