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Commitd87f8c8

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[Doc] Improvements of tempbuffers doc
Clareifed calculation of temp relation size
1 parentde39723 commitd87f8c8

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3 files changed

+35
-1
lines changed

3 files changed

+35
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lines changed

‎doc/src/sgml/func.sgml

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@@ -18865,6 +18865,16 @@ postgres=# SELECT * FROM pg_xlogfile_name_offset(pg_stop_backup());
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Shorthand for <literal>pg_relation_size(..., 'main')</literal>
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</entry>
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</row>
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<row>
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<entry>
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<literal><function>pg_temp_relation_size(<parameter>relation</parameter> <type>regclass</type>)</function></literal>
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</entry>
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<entry><type>bigint</type></entry>
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<entry>
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Total space used by <literal>'main'</literal> fork of
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the specified temporary table.
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</entry>
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</row>
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<row>
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<entry>
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<literal><function>pg_size_bytes(<type>text</type>)</function></literal>
@@ -19004,6 +19014,15 @@ postgres=# SELECT * FROM pg_xlogfile_name_offset(pg_stop_backup());
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</itemizedlist>
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</para>
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<para>
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<function>pg_temp_relation_size</> accepts the OID or name of a temporary table
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and returns the total size in bytes of <literal>'main'</literal> fork of
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that relation. We extend physical file for a temporary table when table doesn't
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fit into <literal>temp_buffers</literal> cache anymore. So total and on-disk size of a temporary
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table can differ. For other kinds of relations it will not throw any error,
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just return NULL.
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</para>
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<para>
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<function>pg_size_pretty</> can be used to format the result of one of
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the other functions in a human-readable way, using bytes, kB, MB, GB or TB

‎doc/src/sgml/ref/create_table.sgml

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@@ -151,6 +151,15 @@ CREATE [ [ GLOBAL | LOCAL ] { TEMPORARY | TEMP } | UNLOGGED | CONSTANT ] TABLE [
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table are automatically temporary as well.
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</para>
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<para>
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Unlike for permanent tables, we extend physical file for a temporary table
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only when it doesn't fit into <literal>temp_buffers</> cache anymore.
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So total and on-disk size of a temporary table can differ. Blocks are
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not allocated in advance, so we may run out of free space on disk
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when trying to evict a temp buffer from cache. It will cause an error.
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This case is quite unusual, though.
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</para>
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<para>
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The <link linkend="autovacuum">autovacuum daemon</link> cannot
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access and therefore cannot vacuum or analyze temporary tables.

‎src/backend/utils/adt/dbsize.c

Lines changed: 7 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -348,13 +348,19 @@ pg_temp_relation_size(PG_FUNCTION_ARGS)
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PG_RETURN_NULL();
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size=0;
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if (rel->rd_rel->relpersistence==RELPERSISTENCE_TEMP)
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if (rel->rd_rel->relpersistence==RELPERSISTENCE_TEMP
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&&rel->rd_rel->relkind==RELKIND_RELATION)
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{
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RelationOpenSmgr(rel);
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if (rel->rd_smgr->smgr_main_nblocks!=InvalidBlockNumber)
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size=BLCKSZ*rel->rd_smgr->smgr_main_nblocks;
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}
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else
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{
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relation_close(rel,AccessShareLock);
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PG_RETURN_NULL();
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}
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relation_close(rel,AccessShareLock);
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