diff options
| -rw-r--r-- | doc/src/sgml/storage.sgml | 11 |
1 files changed, 6 insertions, 5 deletions
diff --git a/doc/src/sgml/storage.sgml b/doc/src/sgml/storage.sgml index 3234adb639f..bfccda77afd 100644 --- a/doc/src/sgml/storage.sgml +++ b/doc/src/sgml/storage.sgml @@ -394,9 +394,9 @@ Further details appear in <xref linkend="storage-toast-inmemory"/>. <para> The compression technique used for either in-line or out-of-line compressed -data is a fairly simple and very fast member -of the LZ family of compression techniques. See -<filename>src/common/pg_lzcompress.c</filename> for the details. +data can be selected using the <literal>COMPRESSION</literal> option on a per-column +basis when creating a table. The default for columns with no explicit setting +is taken from the value of <xref linkend="guc-default-toast-compression" />. </para> <sect2 id="storage-toast-ondisk"> @@ -425,8 +425,9 @@ retrieval of the values. A pointer datum representing an out-of-line on-disk <acronym>TOAST</acronym>ed value therefore needs to store the OID of the <acronym>TOAST</acronym> table in which to look and the OID of the specific value (its <structfield>chunk_id</structfield>). For convenience, pointer datums also store the -logical datum size (original uncompressed data length) and physical stored size -(different if compression was applied). Allowing for the varlena header bytes, +logical datum size (original uncompressed data length), physical stored size +(different if compression was applied), and the compression method used, if +any. Allowing for the varlena header bytes, the total size of an on-disk <acronym>TOAST</acronym> pointer datum is therefore 18 bytes regardless of the actual size of the represented value. </para> |