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Document txid functions.
Marko Kreen
1 parent a06ce21 commit ec1aafc

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‎doc/src/sgml/datatype.sgml

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<!-- $PostgreSQL: pgsql/doc/src/sgml/datatype.sgml,v 1.212 2007/11/05 12:02:20 darcy Exp $ -->
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<!-- $PostgreSQL: pgsql/doc/src/sgml/datatype.sgml,v 1.213 2007/11/05 14:51:08 momjian Exp $ -->
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<chapter id="datatype">
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<title id="datatype-title">Data Types</title>
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</sect1>
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<sect1 id="datatype-txid-snapshot">
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<title>Transaction Snapshot Type</title>
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<indexterm zone="datatype-txid-snapshot">
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<primary>txid_snapshot</primary>
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</indexterm>
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<para>
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The data type <type>txid_snapshot</type> stores info about transaction ID
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visibility at a particular moment in time. The components are
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described in <xref linkend="datatype-txid-snapshot-parts">.
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</para>
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<table id="datatype-txid-snapshot-parts">
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<title>Snapshot components</title>
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<tgroup cols="2">
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<thead>
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<row>
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<entry>Name</entry>
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<entry>Query Function</entry>
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<entry>Description</entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry><type>xmin</type></entry>
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<entry>txid_snapshot_xmin()</entry>
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<entry>
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Earliest transaction ID that is still active. All earlier
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transactions will either be committed and visible, or rolled
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back and dead.
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</entry>
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</row>
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<row>
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<entry><type>xmax</type></entry>
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<entry>txid_snapshot_xmax()</entry>
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<entry>
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Next unassigned txid. All txids later than this one are
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unassigned, and thus invisible.
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</entry>
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</row>
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<row>
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<entry><type>xip_list</type></entry>
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<entry>txid_snapshot_xip()</entry>
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<entry>
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Active txids at the time of snapshot. All of them are between
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xmin and xmax. A txid that is <literal>xmin &lt;= txid &lt;
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xmax</literal> and not in this list is visible.
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</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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<para>
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Snapshot's textual representation is <literal>[xmin]:[xmax]:[xip_list]</literal>
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for example <literal>10:20:10,14,15</literal> means
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<literal>xmin=10 xmax=20 xip_list=10,14,15</literal>.
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</para>
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<para>
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Functions for getting and querying transaction ids and snapshots are
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described in <xref linkend="functions-txid">.
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</para>
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</sect1>
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<sect1 id="datatype-uuid">
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<title><acronym>UUID</acronym> Type</title>
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‎doc/src/sgml/func.sgml

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<!-- $PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.406 2007/10/30 19:06:56 tgl Exp $ -->
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<!-- $PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.407 2007/11/05 14:51:08 momjian Exp $ -->
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<chapter id="functions">
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<title>Functions and Operators</title>
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as well.
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</para>
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</sect1>
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<sect1 id="functions-txid">
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<title>Transaction ID and Snapshot Functions</title>
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<indexterm>
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<primary>txid_current</primary>
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</indexterm>
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</table>
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<para>
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The internal transaction ID type (<type>xid</>) is 32 bits wide and so
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it wraps around every 4 billion transactions. However, these functions
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export a 64-bit format that is extended with an <quote>epoch</> counter
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so that it will not wrap around for the life of an installation.
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The internal transaction ID type (<type>xid</>) is 32 bits wide and
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so it wraps around every 4 billion transactions. However, these
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functions export a 64-bit format that is extended with an
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<quote>epoch</> counter so that it will not wrap around for the life
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of an installation. The main use of these functions is to determine
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which transactions were committed between two snapshots.
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</para>
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</sect1>
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<sect1 id="functions-admin">
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<title>System Administration Functions</title>
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<sect1 id="functions-admin">
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<title>System Administration Functions</title>
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<para>
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<xref linkend="functions-admin-set-table"> shows the functions
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available to query and alter run-time configuration parameters.
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</para>
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<para>
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<xref linkend="functions-admin-set-table"> shows the functions
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available to query and alter run-time configuration parameters.
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</para>
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<table id="functions-admin-set-table">
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<title>Configuration Settings Functions</title>

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