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| author | Simon Riggs | 2017-11-27 09:51:51 +0000 |
|---|---|---|
| committer | Simon Riggs | 2017-11-27 09:51:51 +0000 |
| commit | 117469006bf525c6e8dc84cb9fcbdc4c1a050878 (patch) | |
| tree | b06a6ca6cd6f5787062be7a32a2cb018eae6b5ec /doc/src/sgml/storage.sgml | |
| parent | 59af8d4384ba5ae72986eab7e5cdc514a969aa05 (diff) | |
Additional docs for toast_tuple_target changes
Diffstat (limited to 'doc/src/sgml/storage.sgml')
| -rw-r--r-- | doc/src/sgml/storage.sgml | 7 |
1 files changed, 6 insertions, 1 deletions
diff --git a/doc/src/sgml/storage.sgml b/doc/src/sgml/storage.sgml index 128b19cbc98..c0e548fa5bc 100644 --- a/doc/src/sgml/storage.sgml +++ b/doc/src/sgml/storage.sgml @@ -429,7 +429,7 @@ when a row value to be stored in a table is wider than <symbol>TOAST_TUPLE_THRESHOLD</symbol> bytes (normally 2 kB). The <acronym>TOAST</acronym> code will compress and/or move field values out-of-line until the row value is shorter than -<symbol>TOAST_TUPLE_TARGET</symbol> bytes (also normally 2 kB) +<symbol>TOAST_TUPLE_TARGET</symbol> bytes (also normally 2 kB, adjustable) or no more gains can be had. During an UPDATE operation, values of unchanged fields are normally preserved as-is; so an UPDATE of a row with out-of-line values incurs no <acronym>TOAST</acronym> costs if @@ -484,6 +484,11 @@ with <link linkend="sql-altertable"><command>ALTER TABLE ... SET STORAGE</comman </para> <para> +<symbol>TOAST_TUPLE_TARGET</symbol> can be adjusted for each table using +<link linkend="sql-altertable"><command>ALTER TABLE ... SET (toast_tuple_target = N)</command></link> +</para> + +<para> This scheme has a number of advantages compared to a more straightforward approach such as allowing row values to span pages. Assuming that queries are usually qualified by comparisons against relatively small key values, most of |