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| -rw-r--r-- | doc/src/sgml/storage.sgml | 16 |
1 files changed, 11 insertions, 5 deletions
diff --git a/doc/src/sgml/storage.sgml b/doc/src/sgml/storage.sgml index 2e1914b95b1..61250799ec0 100644 --- a/doc/src/sgml/storage.sgml +++ b/doc/src/sgml/storage.sgml @@ -1122,11 +1122,17 @@ data. Empty in ordinary tables.</entry> </listitem> <listitem> <para> - Old versions of updated rows can be completely removed during normal - operation, including <command>SELECT</command>s, instead of requiring - periodic vacuum operations. (This is possible because indexes - do not reference their <link linkend="storage-page-layout">page - item identifiers</link>.) + When a row is updated multiple times, row versions other than the oldest + and the newest can be completely removed during normal operation, + including <command>SELECT</command>s, instead of requiring periodic vacuum + operations. (Indexes always refer to the + <link linkend="storage-page-layout">page item identifier</link> of the + original row version. The tuple data associated with that row version + is removed, and its item identifier is converted to a redirect that + points to the oldest version that may still be visible to some concurrent + transaction. Intermediate row versions that are no longer visible to + anyone are completely removed, and the associated page item identifiers + are made available for reuse.) </para> </listitem> </itemizedlist> |