</glossdef>

</glossentry>

<glossentry id="glossary-buffer-access-strategy">

<glossterm>Buffer Access Strategy</glossterm>

<glossdef>

<para>

Some operations will access a large number of

<glossterm linkend="glossary-data-page">pages</glossterm>. A

<firstterm>Buffer Access Strategy</firstterm> helps to prevent these

operations from evicting too many pages from

<glossterm linkend="glossary-shared-memory">shared buffers</glossterm>.

</para>

<para>

A Buffer Access Strategy sets up references to a limited number of

<glossterm linkend="glossary-shared-memory">shared buffers</glossterm> and

reuses them circularly. When the operation requires a new page, a victim

buffer is chosen from the buffers in the strategy ring, which may require

flushing the page's dirty data and possibly also unflushed

<glossterm linkend="glossary-wal">WAL</glossterm> to permanent storage.

</para>

<para>

Buffer Access Strategies are used for various operations such as

sequential scans of large tables, <command>VACUUM</command>,

<command>COPY</command>, <command>CREATE TABLE AS SELECT</command>,

<command>ALTER TABLE</command>, <command>CREATE DATABASE</command>,

<command>CREATE INDEX</command>, and <command>CLUSTER</command>.

</para>

</glossdef>

</glossentry>

<glossentry id="glossary-cast">

<glossterm>Cast</glossterm>

<glossdef>