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Minor editorial improvements to txid functions' documentation: put back 

some text that got dropped, improve markup, improve descriptions of
snapshot components.
This commit is contained in:
Tom Lane 2007-11-05 17:40:21 +00:00
parent c00055ea80
commit faac769a6b
1 changed files with 29 additions and 28 deletions
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57
doc/src/sgml/func.sgml
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@ -1,4 +1,4 @@
<!-- $PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.409 2007/11/05 16:57:23 momjian Exp $ -->
<!-- $PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.410 2007/11/05 17:40:21 tgl Exp $ -->
<chapter id="functions">
<title>Functions and Operators</title>
@ -11514,6 +11514,13 @@ SELECT pg_type_is_visible('myschema.widget'::regtype);
<primary>txid_visible_in_snapshot</primary>
</indexterm>
<para>
The functions shown in <xref linkend="functions-txid-snapshot">
export server internal transaction information to user level. The main
use of these functions is to determine which transactions were committed
between two snapshots.
</para>
<table id="functions-txid-snapshot">
<title>Transaction IDs and snapshots</title>
<tgroup cols="3">
@ -11557,27 +11564,22 @@ SELECT pg_type_is_visible('myschema.widget'::regtype);
</table>
<para>
The internal transaction ID type (<type>xid</>) is 32 bits wide and
so it wraps around every 4 billion transactions. However, these
functions export a 64-bit format that is extended with an
<quote>epoch</> counter so that it will not wrap around for the life
of an installation. The main use of these functions is to determine
which transactions were committed between two snapshots.
The internal transaction ID type (<type>xid</>) is 32 bits wide and so
it wraps around every 4 billion transactions. However, these functions
export a 64-bit format that is extended with an <quote>epoch</> counter
so that it will not wrap around for the life of an installation.
The data type used by these functions, <type>txid_snapshot</type>,
stores information about transaction ID
visibility at a particular moment in time. Its components are
described in <xref linkend="functions-txid-snapshot-parts">.
</para>
<para>
The data type <type>txid_snapshot</type> stores info about transaction ID
visibility at a particular moment in time. The components are
described in <xref linkend="datatype-txid-snapshot-parts">.
</para>
<table id="datatype-txid-snapshot-parts">
<table id="functions-txid-snapshot-parts">
<title>Snapshot components</title>
<tgroup cols="2">
<thead>
<row>
<entry>Name</entry>
<entry>Query Function</entry>
<entry>Description</entry>
</row>
</thead>
@ -11586,9 +11588,8 @@ SELECT pg_type_is_visible('myschema.widget'::regtype);
<row>
<entry><type>xmin</type></entry>
<entry>txid_snapshot_xmin()</entry>
<entry>
Earliest transaction ID that is still active. All earlier
Earliest transaction ID (txid) that is still active. All earlier
transactions will either be committed and visible, or rolled
back and dead.
</entry>
@ -11596,20 +11597,20 @@ SELECT pg_type_is_visible('myschema.widget'::regtype);
<row>
<entry><type>xmax</type></entry>
<entry>txid_snapshot_xmax()</entry>
<entry>
Next unassigned txid. All txids later than this one are
unassigned, and thus invisible.
First as-yet-unassigned txid. All txids later than this one are
not yet started as of the time of the snapshot, and thus invisible.
</entry>
</row>
<row>
<entry><type>xip_list</type></entry>
<entry>txid_snapshot_xip()</entry>
<entry>
Active txids at the time of snapshot. All of them are between
xmin and xmax. A txid that is <literal>xmin &lt;= txid &lt;
xmax</literal> and not in this list is visible.
Active txids at the time of the snapshot. All of them are between
<literal>xmin</> and <literal>xmax</>. A txid that is
<literal>xmin &lt;= txid &lt; xmax</literal> and not in this list was
already completed at the time of the snapshot, and thus either visible
or dead according to its commit status.
</entry>
</row>
@ -11618,11 +11619,11 @@ SELECT pg_type_is_visible('myschema.widget'::regtype);
</table>
<para>
Snapshot's textual representation is <literal>[xmin]:[xmax]:[xip_list]</literal>
for example <literal>10:20:10,14,15</literal> means
<literal>xmin=10 xmax=20 xip_list=10,14,15</literal>.
<type>txid_snapshot</>'s textual representation is
<literal><replaceable>xmin</>:<replaceable>xmax</>:<replaceable>xip_list</></literal>.
For example <literal>10:20:10,14,15</literal> means
<literal>xmin=10, xmax=20, xip_list=10, 14, 15</literal>.
</para>
</sect1>
<sect1 id="functions-admin">