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Add note about how to make the SRF detoasted arguments live accross calls.

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Andrew Gierth and Ali Akbar
This commit is contained in:
Fujii Masao 2015-02-26 15:48:07 +09:00
parent f5ef00aed4
commit a7920b872f
1 changed files with 14 additions and 0 deletions
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14
doc/src/sgml/xfunc.sgml
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@ -2981,6 +2981,20 @@ SRF_RETURN_DONE(funcctx)
<structfield>multi_call_memory_ctx</> while doing the first-call setup.
</para>
<warning>
<para>
While the actual arguments to the function remain unchanged between
calls, if you detoast the argument values (which is normally done
transparently by the
<function>PG_GETARG_<replaceable>xxx</replaceable></function> macro)
in the transient context then the detoasted copies will be freed on
each cycle. Accordingly, if you keep references to such values in
your <structfield>user_fctx</>, you must either copy them into the
<structfield>multi_call_memory_ctx</> after detoasting, or ensure
that you detoast the values only in that context.
</para>
</warning>
<para>
A complete pseudo-code example looks like the following:
<programlisting>