Setting this parameter to zero (which is the default) disables the prepared-transaction feature. Sets the maximum number of transactions that can be in the "prepared" state simultaneously (see PREPARE TRANSACTION). However if a buffer is actually used an additional 8192 bytes will be consumed for it (or in general, BLCKSZ bytes). The cost of setting a large value in sessions that do not actually need many temporary buffers is only a buffer descriptor, or about 64 bytes, per increment in temp_buffers. The setting can be changed within individual sessions, but only before the first use of temporary tables within the session subsequent attempts to change the value will have no effect on that session.Ī session will allocate temporary buffers as needed up to the limit given by temp_buffers. These are session-local buffers used only for access to temporary tables. Sets the maximum number of temporary buffers used by each database session. With on, failure to use huge pages will prevent the server from starting up. With huge_pages set to try, the server will try to use huge pages, but fall back to using normal allocation if that fails. The use of huge pages results in smaller page tables and less CPU time spent on memory management, increasing performance.
The setting is ignored on other systems when set to try. Valid values are try (the default), on, and off.Īt present, this feature is supported only on Linux. huge_pages ( enum)Įnables/disables the use of huge memory pages.
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The useful range for shared_buffers on Windows systems is generally from 64MB to 512MB. You may find better results keeping the setting relatively low and using the operating system cache more instead. Also, on Windows, large values for shared_buffers aren't as effective. 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. 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. There are some workloads where even large 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. 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. This parameter can only be set at server start. (Non-default values of BLCKSZ change the minimum.) However, settings significantly higher than the minimum are usually needed for good performance. This setting must be at least 128 kilobytes. The default is typically 128 megabytes ( 128MB), but might be less if your kernel settings will not support it (as determined during initdb). Sets the amount of memory the database server uses for shared memory buffers.