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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.
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