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Type: integer
Default: 1024
Min: 16
Max: 1073741823
Unit: 8kB
Context: postmaster
Restart: true

Sets the amount of memory the database server uses for shared memory buffers. The default is typically 128 megabytes (128MB), but might be less if your kernel settings will not support it (as determined during initdb). This setting must be at least 128 kilobytes. However, settings significantly higher than the minimum are usually needed for good performance. If this value is specified without units, it is taken as blocks, that is BLCKSZ bytes, typically 8kB. (Non-default values of BLCKSZ change the minimum value.) This parameter can only be set at server start.

If you have a dedicated database server with 1GB or more of RAM, a reasonable starting value for shared_buffers is 25% of the memory in your system. There are some workloads where even larger settings for shared_buffers are effective, but because PostgreSQL also relies on the operating system cache, it is unlikely that an allocation of more than 40% of RAM to shared_buffers will work better than a smaller amount. Larger settings for shared_buffers usually require a corresponding increase in max_wal_size, in order to spread out the process of writing large quantities of new or changed data over a longer period of time.

On systems with less than 1GB of RAM, a smaller percentage of RAM is appropriate, so as to leave adequate space for the operating system.

Recommendations

A memory quantity defining PostgreSQL's "dedicated" RAM, which is used for connection control, active operations, and more. However, since PostgreSQL also needs free RAM for file system buffers, sorts and maintenance operations, it is not advisable to set shared_buffers to a majority of RAM. Note that increasing shared_buffers often requires you to increase some system kernel parameters, most notably SHMMAX and SHMALL. See Operating System Environment: Managing Kernel Resources in the PostgreSQL documentation for more details. Also note that shared_buffers over 2GB is only supported on 64-bit systems.

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