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Commit16a6912

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Warn more vigorously about the non-transactional behavior of sequences.
Craig Ringer, edited fairly heavily by me
1 parent3159599 commit16a6912

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2 files changed

+42
-20
lines changed

2 files changed

+42
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lines changed

‎doc/src/sgml/datatype.sgml

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@@ -802,6 +802,20 @@ ALTER SEQUENCE <replaceable class="parameter">tablename</replaceable>_<replaceab
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the column, so that it will be dropped if the column or table is dropped.
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</para>
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<note>
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<para>
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Because <type>smallserial</type>, <type>serial</type> and
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<type>bigserial</type> are implemented usings sequences, there may
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be "holes" or gaps in the sequence of values which appears in the
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column, even if no rows are ever deleted. This is a value allocated
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from the sequence is still "used up" even if a row containing that
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value is never successfully inserted into the table column. This
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may happen, for example, if the inserting transaction rolls back.
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See <literal>nextval()</literal> in <xref linkend="functions-sequence">
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for details.
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</para>
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</note>
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<note>
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<para>
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Prior to <productname>PostgreSQL</productname> 7.3, <type>serial</type>

‎doc/src/sgml/func.sgml

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@@ -9741,6 +9741,27 @@ nextval('foo'::text) <lineannotation><literal>foo</literal> is looked up at
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execute <function>nextval</function> concurrently, each will safely receive
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a distinct sequence value.
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</para>
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<para>
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If a sequence object has been created with default parameters,
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successive <function>nextval</function> calls will return successive
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values beginning with 1. Other behaviors can be obtained by using
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special parameters in the <xref linkend="sql-createsequence"> command;
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see its command reference page for more information.
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</para>
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<important>
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<para>
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To avoid blocking concurrent transactions that obtain numbers from the
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same sequence, a <function>nextval</function> operation is never
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rolled back; that is, once a value has been fetched it is considered
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used, even if the transaction that did the
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<function>nextval</function> later aborts. This means that aborted
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transactions might leave unused <quote>holes</quote> in the sequence
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of assigned values.
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</para>
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</important>
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</listitem>
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</varlistentry>
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@@ -9804,31 +9825,18 @@ SELECT setval('foo', 42, false); <lineannotation>Next <function>nextval</> wi
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The result returned by <function>setval</function> is just the value of its
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second argument.
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</para>
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<important>
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<para>
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Because sequences are non-transactional, changes made by
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<function>setval</function> are not undone if the transaction rolls
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back.
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</para>
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</important>
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</listitem>
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</varlistentry>
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</variablelist>
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</para>
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<para>
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If a sequence object has been created with default parameters,
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successive <function>nextval</function> calls will return successive values
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beginning with 1. Other behaviors can be obtained by using
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special parameters in the <xref linkend="sql-createsequence"> command;
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see its command reference page for more information.
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</para>
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<important>
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<para>
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To avoid blocking concurrent transactions that obtain numbers from the
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same sequence, a <function>nextval</function> operation is never rolled back;
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that is, once a value has been fetched it is considered used, even if the
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transaction that did the <function>nextval</function> later aborts. This means
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that aborted transactions might leave unused <quote>holes</quote> in the
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sequence of assigned values. <function>setval</function> operations are never
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rolled back, either.
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</para>
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</important>
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</sect1>
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