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Commita0899c0

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Doc: minor improvements for plpgsql "Transaction Management" section.
Point out that savepoint commands cannot be issued in PL/pgSQL,and suggest that exception blocks can usually be used instead.Add a caveat to the discussion of cursor loops vs. transactions,pointing out that any locks taken by the cursor query will be lostat COMMIT. This is implicit in what's already said, but the existingtext leaves the distinct impression that the auto-hold behavior istransparent, which it's not really.Per a couple of recent complaints (one unsigned, and one in bug #18531from Dzmitry Jachnik). Back-patch to v17, just so this makes it intocurrent docs in less than a year-and-a-half.Discussion:https://postgr.es/m/172076354433.736586.14347210271966220018@wrigleys.postgresql.orgDiscussion:https://postgr.es/m/18531-c6dddd33b8555fd2@postgresql.org
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‎doc/src/sgml/plpgsql.sgml

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@@ -3745,6 +3745,17 @@ CALL transaction_test1();
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<command>SELECT</command> in between.
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</para>
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<para>
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<application>PL/pgSQL</application> does not support savepoints
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(<command>SAVEPOINT</command>/<command>ROLLBACK TO
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SAVEPOINT</command>/<command>RELEASE SAVEPOINT</command> commands).
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Typical usage patterns for savepoints can be replaced by blocks with
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exception handlers (see <xref linkend="plpgsql-error-trapping"/>).
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Under the hood, a block with exception handlers forms a
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subtransaction, which means that transactions cannot be ended inside
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such a block.
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</para>
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<para>
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Special considerations apply to cursor loops. Consider this example:
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<programlisting>
@@ -3770,18 +3781,17 @@ CALL transaction_test2();
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evaluated at the first <command>COMMIT</command> or
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<command>ROLLBACK</command> rather than row by row. The cursor is still
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removed automatically after the loop, so this is mostly invisible to the
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user.
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user. But one must keep in mind that any table or row locks taken by
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the cursor's query will no longer be held after the
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first <command>COMMIT</command> or
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<command>ROLLBACK</command>.
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</para>
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<para>
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Transaction commands are not allowed in cursor loops driven by commands
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that are not read-only (for example <command>UPDATE
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... RETURNING</command>).
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</para>
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<para>
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A transaction cannot be ended inside a block with exception handlers.
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</para>
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</sect1>
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<sect1 id="plpgsql-errors-and-messages">

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