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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>74.2. Transactions and Locking</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot" /><link rel="prev" href="transaction-id.html" title="74.1. Transactions and Identifiers" /><link rel="next" href="subxacts.html" title="74.3. Subtransactions" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">74.2. Transactions and Locking</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="transaction-id.html" title="74.1. Transactions and Identifiers">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="transactions.html" title="Chapter 74. Transaction Processing">Up</a></td><th width="60%" align="center">Chapter 74. Transaction Processing</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 16.2 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="subxacts.html" title="74.3. Subtransactions">Next</a></td></tr></table><hr /></div><div class="sect1" id="XACT-LOCKING"><div class="titlepage"><div><div><h2 class="title" style="clear: both">74.2. Transactions and Locking <a href="#XACT-LOCKING" class="id_link">#</a></h2></div></div></div><p>
The transaction IDs of currently executing transactions are shown in
<a class="link" href="view-pg-locks.html" title="54.12. pg_locks"><code class="structname">pg_locks</code></a>
in columns <code class="structfield">virtualxid</code> and
<code class="structfield">transactionid</code>. Read-only transactions
will have <code class="structfield">virtualxid</code>s but NULL
<code class="structfield">transactionid</code>s, while both columns will be
set in read-write transactions.
</p><p>
Some lock types wait on <code class="structfield">virtualxid</code>,
while other types wait on <code class="structfield">transactionid</code>.
Row-level read and write locks are recorded directly in the locked
rows and can be inspected using the <a class="xref" href="pgrowlocks.html" title="F.31. pgrowlocks — show a table's row locking information">pgrowlocks</a>
extension. Row-level read locks might also require the assignment
of multixact IDs (<code class="literal">mxid</code>; see <a class="xref" href="routine-vacuuming.html#VACUUM-FOR-MULTIXACT-WRAPAROUND" title="25.1.5.1. Multixacts and Wraparound">Section 25.1.5.1</a>).
</p></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="transaction-id.html" title="74.1. Transactions and Identifiers">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="transactions.html" title="Chapter 74. Transaction Processing">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="subxacts.html" title="74.3. Subtransactions">Next</a></td></tr><tr><td width="40%" align="left" valign="top">74.1. Transactions and Identifiers </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 16.2 Documentation">Home</a></td><td width="40%" align="right" valign="top"> 74.3. Subtransactions</td></tr></table></div></body></html>
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