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Postfix Documentation
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Tweaking performance

Postfix provides two configuration parameters that control how much buffering memory Berkeley DB will use.

  • berkeley_db_create_buffer_size (default: 16 MBytes per table). This setting is used by the commands that maintain Berkeley DB files: postalias(1) and postmap(1). For "hash" files, create performance degrades rapidly unless the memory pool is O(file size). For "btree" files, create performance is good with sorted input even for small memory pools, but with random input degrades rapidly unless the memory pool is O(file size).

  • berkeley_db_read_buffer_size (default: 128 kBytes per table). This setting is used by all other Postfix programs. The buffer size is adequate for reading. If the cache is smaller than the table, random read performance is hardly cache size dependent, except with btree tables, where the cache size must be large enough to contain the entire path from the root node. Empirical evidence shows that 64 kBytes may be sufficient. We double the size to play safe, and to anticipate changes in implementation and bloat.

Postfix Documentation
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