<?xml version="1.0" encoding="UTF-8" standalone="no"?> <!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>70.3. 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="70.2. Multivariate Statistics Examples" /><link rel="next" href="appendixes.html" title="Part VIII. Appendixes" /></head><body><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">70.3. Planner Statistics and Security</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="multivariate-statistics-examples.html" title="70.2. Multivariate Statistics Examples">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="planner-stats-details.html" title="Chapter 70. How the Planner Uses Statistics">Up</a></td><th width="60%" align="center">Chapter 70. How the Planner Uses Statistics</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 11.5 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="appendixes.html" title="Part VIII. Appendixes">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="PLANNER-STATS-SECURITY"><div class="titlepage"><div><div><h2 class="title" style="clear: both">70.3. 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">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="planner-stats-details.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="appendixes.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">70.2. Multivariate Statistics Examples </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> Part VIII. Appendixes</td></tr></table></div></body></html>
