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diff --git a/doc/src/sgml/html/event-trigger-table-rewrite-example.html b/doc/src/sgml/html/event-trigger-table-rewrite-example.html new file mode 100644 index 0000000..14af9a5 --- /dev/null +++ b/doc/src/sgml/html/event-trigger-table-rewrite-example.html @@ -0,0 +1,48 @@ +<?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>39.5. A Table Rewrite Event Trigger Example</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 V1.79.1" /><link rel="prev" href="event-trigger-example.html" title="39.4. A Complete Event Trigger Example" /><link rel="next" href="rules.html" title="Chapter 40. The Rule System" /></head><body id="docContent" class="container-fluid col-10"><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">39.5. A Table Rewrite Event Trigger Example</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="event-trigger-example.html" title="39.4. A Complete Event Trigger Example">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="event-triggers.html" title="Chapter 39. Event Triggers">Up</a></td><th width="60%" align="center">Chapter 39. Event Triggers</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 13.4 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="rules.html" title="Chapter 40. The Rule System">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="EVENT-TRIGGER-TABLE-REWRITE-EXAMPLE"><div class="titlepage"><div><div><h2 class="title" style="clear: both">39.5. A Table Rewrite Event Trigger Example</h2></div></div></div><p> + Thanks to the <code class="literal">table_rewrite</code> event, it is possible to implement + a table rewriting policy only allowing the rewrite in maintenance windows. + </p><p> + Here's an example implementing such a policy. +</p><pre class="programlisting"> +CREATE OR REPLACE FUNCTION no_rewrite() + RETURNS event_trigger + LANGUAGE plpgsql AS +$$ +--- +--- Implement local Table Rewriting policy: +--- public.foo is not allowed rewriting, ever +--- other tables are only allowed rewriting between 1am and 6am +--- unless they have more than 100 blocks +--- +DECLARE + table_oid oid := pg_event_trigger_table_rewrite_oid(); + current_hour integer := extract('hour' from current_time); + pages integer; + max_pages integer := 100; +BEGIN + IF pg_event_trigger_table_rewrite_oid() = 'public.foo'::regclass + THEN + RAISE EXCEPTION 'you''re not allowed to rewrite the table %', + table_oid::regclass; + END IF; + + SELECT INTO pages relpages FROM pg_class WHERE oid = table_oid; + IF pages > max_pages + THEN + RAISE EXCEPTION 'rewrites only allowed for table with less than % pages', + max_pages; + END IF; + + IF current_hour NOT BETWEEN 1 AND 6 + THEN + RAISE EXCEPTION 'rewrites only allowed between 1am and 6am'; + END IF; +END; +$$; + +CREATE EVENT TRIGGER no_rewrite_allowed + ON table_rewrite + EXECUTE FUNCTION no_rewrite(); +</pre><p> + </p></div><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navfooter"><hr></hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="event-trigger-example.html" title="39.4. A Complete Event Trigger Example">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="event-triggers.html" title="Chapter 39. Event Triggers">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="rules.html" title="Chapter 40. The Rule System">Next</a></td></tr><tr><td width="40%" align="left" valign="top">39.4. A Complete Event Trigger Example </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 13.4 Documentation">Home</a></td><td width="40%" align="right" valign="top"> Chapter 40. The Rule System</td></tr></table></div></body></html>
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