diff options
Diffstat (limited to '')
| -rw-r--r-- | www/c3ref/autovacuum_pages.html | 189 |
1 files changed, 189 insertions, 0 deletions
diff --git a/www/c3ref/autovacuum_pages.html b/www/c3ref/autovacuum_pages.html new file mode 100644 index 0000000..cba4622 --- /dev/null +++ b/www/c3ref/autovacuum_pages.html @@ -0,0 +1,189 @@ +<!DOCTYPE html> +<html><head> +<meta name="viewport" content="width=device-width, initial-scale=1.0"> +<meta http-equiv="content-type" content="text/html; charset=UTF-8"> +<link href="../sqlite.css" rel="stylesheet"> +<title>Autovacuum Compaction Amount Callback</title> +<!-- path=../ --> +</head> +<body> +<div class=nosearch> +<a href="../index.html"> +<img class="logo" src="../images/sqlite370_banner.gif" alt="SQLite" border="0"> +</a> +<div><!-- IE hack to prevent disappearing logo --></div> +<div class="tagline desktoponly"> +Small. Fast. Reliable.<br>Choose any three. +</div> +<div class="menu mainmenu"> +<ul> +<li><a href="../index.html">Home</a> +<li class='mobileonly'><a href="javascript:void(0)" onclick='toggle_div("submenu")'>Menu</a> +<li class='wideonly'><a href='../about.html'>About</a> +<li class='desktoponly'><a href="../docs.html">Documentation</a> +<li class='desktoponly'><a href="../download.html">Download</a> +<li class='wideonly'><a href='../copyright.html'>License</a> +<li class='desktoponly'><a href="../support.html">Support</a> +<li class='desktoponly'><a href="../prosupport.html">Purchase</a> +<li class='search' id='search_menubutton'> +<a href="javascript:void(0)" onclick='toggle_search()'>Search</a> +</ul> +</div> +<div class="menu submenu" id="submenu"> +<ul> +<li><a href='../about.html'>About</a> +<li><a href='../docs.html'>Documentation</a> +<li><a href='../download.html'>Download</a> +<li><a href='../support.html'>Support</a> +<li><a href='../prosupport.html'>Purchase</a> +</ul> +</div> +<div class="searchmenu" id="searchmenu"> +<form method="GET" action="../search"> +<select name="s" id="searchtype"> +<option value="d">Search Documentation</option> +<option value="c">Search Changelog</option> +</select> +<input type="text" name="q" id="searchbox" value=""> +<input type="submit" value="Go"> +</form> +</div> +</div> +<script> +function toggle_div(nm) { +var w = document.getElementById(nm); +if( w.style.display=="block" ){ +w.style.display = "none"; +}else{ +w.style.display = "block"; +} +} +function toggle_search() { +var w = document.getElementById("searchmenu"); +if( w.style.display=="block" ){ +w.style.display = "none"; +} else { +w.style.display = "block"; +setTimeout(function(){ +document.getElementById("searchbox").focus() +}, 30); +} +} +function div_off(nm){document.getElementById(nm).style.display="none";} +window.onbeforeunload = function(e){div_off("submenu");} +/* Disable the Search feature if we are not operating from CGI, since */ +/* Search is accomplished using CGI and will not work without it. */ +if( !location.origin || !location.origin.match || !location.origin.match(/http/) ){ +document.getElementById("search_menubutton").style.display = "none"; +} +/* Used by the Hide/Show button beside syntax diagrams, to toggle the */ +function hideorshow(btn,obj){ +var x = document.getElementById(obj); +var b = document.getElementById(btn); +if( x.style.display!='none' ){ +x.style.display = 'none'; +b.innerHTML='show'; +}else{ +x.style.display = ''; +b.innerHTML='hide'; +} +return false; +} +var antiRobot = 0; +function antiRobotGo(){ +if( antiRobot!=3 ) return; +antiRobot = 7; +var j = document.getElementById("mtimelink"); +if(j && j.hasAttribute("data-href")) j.href=j.getAttribute("data-href"); +} +function antiRobotDefense(){ +document.body.onmousedown=function(){ +antiRobot |= 2; +antiRobotGo(); +document.body.onmousedown=null; +} +document.body.onmousemove=function(){ +antiRobot |= 2; +antiRobotGo(); +document.body.onmousemove=null; +} +setTimeout(function(){ +antiRobot |= 1; +antiRobotGo(); +}, 100) +antiRobotGo(); +} +antiRobotDefense(); +</script> +<!-- keywords: sqlite3_autovacuum_pages --> +<div class=nosearch> +<a href="intro.html"><h2>SQLite C Interface</h2></a> +<h2>Autovacuum Compaction Amount Callback</h2> +</div> +<blockquote><pre> +int sqlite3_autovacuum_pages( + sqlite3 *db, + unsigned int(*)(void*,const char*,unsigned int,unsigned int,unsigned int), + void*, + void(*)(void*) +); +</pre></blockquote> +<p> +The sqlite3_autovacuum_pages(D,C,P,X) interface registers a callback +function C that is invoked prior to each autovacuum of the database +file. The callback is passed a copy of the generic data pointer (P), +the schema-name of the attached database that is being autovacuumed, +the size of the database file in pages, the number of free pages, +and the number of bytes per page, respectively. The callback should +return the number of free pages that should be removed by the +autovacuum. If the callback returns zero, then no autovacuum happens. +If the value returned is greater than or equal to the number of +free pages, then a complete autovacuum happens.</p> + +<p><p>If there are multiple ATTACH-ed database files that are being +modified as part of a transaction commit, then the autovacuum pages +callback is invoked separately for each file.</p> + +<p><p><b>The callback is not reentrant.</b> The callback function should +not attempt to invoke any other SQLite interface. If it does, bad +things may happen, including segmentation faults and corrupt database +files. The callback function should be a simple function that +does some arithmetic on its input parameters and returns a result.</p> + +<p>The X parameter to sqlite3_autovacuum_pages(D,C,P,X) is an optional +destructor for the P parameter. If X is not NULL, then X(P) is +invoked whenever the database connection closes or when the callback +is overwritten by another invocation of sqlite3_autovacuum_pages().</p> + +<p><p>There is only one autovacuum pages callback per database connection. +Each call to the sqlite3_autovacuum_pages() interface overrides all +previous invocations for that database connection. If the callback +argument (C) to sqlite3_autovacuum_pages(D,C,P,X) is a NULL pointer, +then the autovacuum steps callback is cancelled. The return value +from sqlite3_autovacuum_pages() is normally SQLITE_OK, but might +be some other error code if something goes wrong. The current +implementation will only return SQLITE_OK or SQLITE_MISUSE, but other +return codes might be added in future releases.</p> + +<p><p>If no autovacuum pages callback is specified (the usual case) or +a NULL pointer is provided for the callback, +then the default behavior is to vacuum all free pages. So, in other +words, the default behavior is the same as if the callback function +were something like this:</p> + +<p><blockquote><pre> + unsigned int demonstration_autovac_pages_callback( + void *pClientData, + const char *zSchema, + unsigned int nDbPage, + unsigned int nFreePage, + unsigned int nBytePerPage + ){ + return nFreePage; + } +</pre></blockquote> +</p><p>See also lists of + <a href="objlist.html">Objects</a>, + <a href="constlist.html">Constants</a>, and + <a href="funclist.html">Functions</a>.</p> + |