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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>75.3. Planner Statistics and Security</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="multivariate-statistics-examples.html" title="75.2. Multivariate Statistics Examples" /><link rel="next" href="backup-manifest-format.html" title="Chapter 76. Backup Manifest Format" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">75.3. Planner Statistics and Security</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="multivariate-statistics-examples.html" title="75.2. Multivariate Statistics Examples">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="planner-stats-details.html" title="Chapter 75. How the Planner Uses Statistics">Up</a></td><th width="60%" align="center">Chapter 75. How the Planner Uses Statistics</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 15.5 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="backup-manifest-format.html" title="Chapter 76. Backup Manifest Format">Next</a></td></tr></table><hr /></div><div class="sect1" id="PLANNER-STATS-SECURITY"><div class="titlepage"><div><div><h2 class="title" style="clear: both">75.3. Planner Statistics and Security</h2></div></div></div><p>
+   Access to the table <code class="structname">pg_statistic</code> is restricted to
+   superusers, so that ordinary users cannot learn about the contents of the
+   tables of other users from it.  Some selectivity estimation functions will
+   use a user-provided operator (either the operator appearing in the query or
+   a related operator) to analyze the stored statistics.  For example, in order
+   to determine whether a stored most common value is applicable, the
+   selectivity estimator will have to run the appropriate <code class="literal">=</code>
+   operator to compare the constant in the query to the stored value.
+   Thus the data in <code class="structname">pg_statistic</code> is potentially
+   passed to user-defined operators.  An appropriately crafted operator can
+   intentionally leak the passed operands (for example, by logging them
+   or writing them to a different table), or accidentally leak them by showing
+   their values in error messages, in either case possibly exposing data from
+   <code class="structname">pg_statistic</code> to a user who should not be able to
+   see it.
+  </p><p>
+   In order to prevent this, the following applies to all built-in selectivity
+   estimation functions.  When planning a query, in order to be able to use
+   stored statistics, the current user must either
+   have <code class="literal">SELECT</code> privilege on the table or the involved
+   columns, or the operator used must be <code class="literal">LEAKPROOF</code> (more
+   accurately, the function that the operator is based on).  If not, then the
+   selectivity estimator will behave as if no statistics are available, and
+   the planner will proceed with default or fall-back assumptions.
+  </p><p>
+   If a user does not have the required privilege on the table or columns,
+   then in many cases the query will ultimately receive a permission-denied
+   error, in which case this mechanism is invisible in practice.  But if the
+   user is reading from a security-barrier view, then the planner might wish
+   to check the statistics of an underlying table that is otherwise
+   inaccessible to the user.  In that case, the operator should be leak-proof
+   or the statistics will not be used.  There is no direct feedback about
+   that, except that the plan might be suboptimal.  If one suspects that this
+   is the case, one could try running the query as a more privileged user,
+   to see if a different plan results.
+  </p><p>
+   This restriction applies only to cases where the planner would need to
+   execute a user-defined operator on one or more values
+   from <code class="structname">pg_statistic</code>.  Thus the planner is permitted
+   to use generic statistical information, such as the fraction of null values
+   or the number of distinct values in a column, regardless of access
+   privileges.
+  </p><p>
+   Selectivity estimation functions contained in third-party extensions that
+   potentially operate on statistics with user-defined operators should follow
+   the same security rules.  Consult the PostgreSQL source code for guidance.
+  </p></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="multivariate-statistics-examples.html" title="75.2. Multivariate Statistics Examples">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="planner-stats-details.html" title="Chapter 75. How the Planner Uses Statistics">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="backup-manifest-format.html" title="Chapter 76. Backup Manifest Format">Next</a></td></tr><tr><td width="40%" align="left" valign="top">75.2. Multivariate Statistics Examples </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 15.5 Documentation">Home</a></td><td width="40%" align="right" valign="top"> Chapter 76. Backup Manifest Format</td></tr></table></div></body></html>
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