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Re: Shared memory usage in PostgreSQL 9.1

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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

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