pg_prewarmのインストールと使用
インストール手順:cd contrib/pg_prewarm make make install pg_prewarm.soはlibディレクトリにインストールされます.pg_prewarm--1.0.sqlとpg_prewarm.controlファイルshare/extension/ディレクトリ
psql実行拡張create extension pg_の作成prewarm; キャッシュするテーブルをbufferに追加select pg_prewarm('department_info','buffer');
shared_buffersは少し大きく設定し、テーブルのデータをbufferにロードします.
F.27. pg_prewarm
The pg_prewarm module provides a convenient way to load relation data into either the operating system buffer cache or the PostgreSQL buffer cache.
F.27.1. Functions
pg_prewarm(regclass, mode text default 'buffer', fork text default 'main', first_block int8 default null, last_block int8 default null) RETURNS int8
The first argument is the relation to be prewarmed. The second argument is the prewarming method to be used, as further discussed below; the third is the relation fork to be prewarmed, usuallymain. The fourth argument is the first block number to prewarm (NULL is accepted as a synonym for zero). The fifth argument is the last block number to prewarm (NULL means prewarm through the last block in the relation). The return value is the number of blocks prewarmed.
There are three available prewarming methods.prefetch issues asynchronous prefetch requests to the operating system, if this is supported, or throws an error therwise.read reads the requested range of blocks; unlikeprefetch, this is synchronous and supported on all platforms and builds, but may be slower.buffer reads the requested range of blocks into the database buffer cache.
Note that with any of these methods, attempting to prewarm more blocks than can be cached — by the OS when singprefetch orread, or by PostgreSQL when usingbuffer— will likely result in lower-numbered blocks being evicted as igher numbered blocks are read in. Prewarmed data also enjoys no special protection from cache evictions, so it is ossible for other system activity may evict the newly prewarmed blocks shortly after they are read; conversely, prewarming may also evict other data from cache. For these reasons, prewarming is typically most useful at startup, hen caches are largely empty.