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Clarify that COPY FREEZE is not a hard rule.

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Remove message when FREEZE not honoured,
clarify reasons in comments and docs.
This commit is contained in:
Simon Riggs 2012-12-07 12:59:05 +00:00
parent 31a891857a
commit 1eb6cee499
2 changed files with 10 additions and 8 deletions
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8
doc/src/sgml/ref/copy.sgml
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@ -186,17 +186,19 @@ COPY { <replaceable class="parameter">table_name</replaceable> [ ( <replaceable
<term><literal>FREEZE</literal></term> <term><literal>FREEZE</literal></term>
<listitem> <listitem>
<para> <para>
Specifies copying the data with rows already frozen, just as they Requests copying the data with rows already frozen, just as they
would be after running the <command>VACUUM FREEZE</> command. would be after running the <command>VACUUM FREEZE</> command.
This is intended as a performance option for initial data loading. This is intended as a performance option for initial data loading.
Rows will be frozen only if the table being loaded has been created Rows will be frozen only if the table being loaded has been created
in the current subtransaction, there are no cursors open and there in the current subtransaction, there are no cursors open and there
are no older snapshots held by this transaction. If those conditions are no older snapshots held by this transaction. If those conditions
are not met the command will continue without error though will not are not met the command will continue without error though will not
freeze rows. freeze rows. It is also possible in rare cases that the request
cannot be honoured for internal reasons, hence <literal>FREEZE</literal>
is more of a guideline than a hard rule.
</para> </para>
<para> <para>
Note that all sessions will immediately be able to see the data Note that all other sessions will immediately be able to see the data
once it has been successfully loaded. This violates the normal rules once it has been successfully loaded. This violates the normal rules
of MVCC visibility and by specifying this option the user acknowledges of MVCC visibility and by specifying this option the user acknowledges
explicitly that this is understood. explicitly that this is understood.

10
src/backend/commands/copy.c
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@ -1993,6 +1993,11 @@ CopyFrom(CopyState cstate)
* after xact cleanup. Note that the stronger test of exactly * after xact cleanup. Note that the stronger test of exactly
* which subtransaction created it is crucial for correctness * which subtransaction created it is crucial for correctness
* of this optimisation. * of this optimisation.
*
* Note that because the test is unreliable in case of relcache reset
* we cannot guarantee that we can honour the request to FREEZE.
* If we cannot honour the request we do so silently, firstly to
* avoid noise for the user and also to avoid obscure test failures.
*/ */
if (cstate->freeze && if (cstate->freeze &&
ThereAreNoPriorRegisteredSnapshots() && ThereAreNoPriorRegisteredSnapshots() &&
@ -2001,11 +2006,6 @@ CopyFrom(CopyState cstate)
hi_options |= HEAP_INSERT_FROZEN; hi_options |= HEAP_INSERT_FROZEN;
} }
if (cstate->freeze && (hi_options & HEAP_INSERT_FROZEN) == 0)
ereport(NOTICE,
(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
errmsg("FREEZE option specified but pre-conditions not met")));
/* /*
* We need a ResultRelInfo so we can use the regular executor's * We need a ResultRelInfo so we can use the regular executor's
* index-entry-making machinery. (There used to be a huge amount of code * index-entry-making machinery. (There used to be a huge amount of code