165 lines
5.6 KiB
HTML
165 lines
5.6 KiB
HTML
<!DOCTYPE html>
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<html><head>
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<meta name="viewport" content="width=device-width, initial-scale=1.0">
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<meta http-equiv="content-type" content="text/html; charset=UTF-8">
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<link href="sqlite.css" rel="stylesheet">
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<title>Change in Default Page Size in SQLite Version 3.12.0</title>
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<!-- path= -->
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</head>
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<body>
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<div class=nosearch>
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<a href="index.html">
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<img class="logo" src="images/sqlite370_banner.gif" alt="SQLite" border="0">
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</a>
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<div><!-- IE hack to prevent disappearing logo --></div>
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<div class="tagline desktoponly">
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Small. Fast. Reliable.<br>Choose any three.
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</div>
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<div class="menu mainmenu">
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<ul>
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<li><a href="index.html">Home</a>
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<li class='mobileonly'><a href="javascript:void(0)" onclick='toggle_div("submenu")'>Menu</a>
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<li class='wideonly'><a href='about.html'>About</a>
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<li class='desktoponly'><a href="docs.html">Documentation</a>
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<li class='desktoponly'><a href="download.html">Download</a>
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<li class='wideonly'><a href='copyright.html'>License</a>
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<li class='desktoponly'><a href="support.html">Support</a>
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<li class='desktoponly'><a href="prosupport.html">Purchase</a>
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<li class='search' id='search_menubutton'>
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<a href="javascript:void(0)" onclick='toggle_search()'>Search</a>
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</ul>
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</div>
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<div class="menu submenu" id="submenu">
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<ul>
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<li><a href='about.html'>About</a>
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<li><a href='docs.html'>Documentation</a>
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<li><a href='download.html'>Download</a>
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<li><a href='support.html'>Support</a>
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<li><a href='prosupport.html'>Purchase</a>
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</ul>
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</div>
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<div class="searchmenu" id="searchmenu">
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<form method="GET" action="search">
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<select name="s" id="searchtype">
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<option value="d">Search Documentation</option>
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<option value="c">Search Changelog</option>
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</select>
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<input type="text" name="q" id="searchbox" value="">
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<input type="submit" value="Go">
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</form>
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</div>
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</div>
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<script>
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function toggle_div(nm) {
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var w = document.getElementById(nm);
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if( w.style.display=="block" ){
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w.style.display = "none";
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}else{
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w.style.display = "block";
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}
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}
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function toggle_search() {
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var w = document.getElementById("searchmenu");
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if( w.style.display=="block" ){
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w.style.display = "none";
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} else {
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w.style.display = "block";
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setTimeout(function(){
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document.getElementById("searchbox").focus()
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}, 30);
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}
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}
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function div_off(nm){document.getElementById(nm).style.display="none";}
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window.onbeforeunload = function(e){div_off("submenu");}
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/* Disable the Search feature if we are not operating from CGI, since */
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/* Search is accomplished using CGI and will not work without it. */
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if( !location.origin || !location.origin.match || !location.origin.match(/http/) ){
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document.getElementById("search_menubutton").style.display = "none";
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}
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/* Used by the Hide/Show button beside syntax diagrams, to toggle the */
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function hideorshow(btn,obj){
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var x = document.getElementById(obj);
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var b = document.getElementById(btn);
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if( x.style.display!='none' ){
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x.style.display = 'none';
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b.innerHTML='show';
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}else{
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x.style.display = '';
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b.innerHTML='hide';
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}
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return false;
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}
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</script>
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</div>
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<h1 align="center">The Default Page Size Change of SQLite 3.12.0</h1>
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<h2>1.0 Introduction</h2>
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<p>
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An SQLite database file consists of one or more "pages".
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For a single database file, all pages are the same size, though
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for different database files, the page size can any power of
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two between 512 and 65536, inclusive.
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</p>
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<p>
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Since the SQLite database file format was designed (in 2003) the
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default <a href="pragma.html#pragma_page_size">page size</a> for new databases has been 1024 bytes.
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This was a reasonable choice in 2003. But on modern hardware,
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a 4096 byte page is a faster and better choice.
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So, beginning with SQLite <a href="releaselog/3_12_0.html">version 3.12.0</a> (2016-03-29)) the default
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page size for new database files has been increased to 4096 bytes.
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</p>
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<p>
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The upper bound on the database <a href="pragma.html#pragma_cache_size">cache size</a> has
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traditionally defaulted to 2000 pages. SQLite <a href="releaselog/3_12_0.html">version 3.12.0</a> also
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changes this default setting to be "-2000" which means 2000*1024
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bytes, regardless of page size. So, the upper bound on the amount
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of memory used for the page cache is unchanged.
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</p>
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<h2>2.0 <u>Not</u> a Compatibility Break</h2>
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<p>
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These changes in the default behavior of SQLite are not
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a compatibility break. All legacy database files continue to be
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readable and writable by newer versions of SQLite, and all newly
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created database files continue to be readable and writable by
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legacy versions of the SQLite library. The only thing that is changing
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is some default settings. This should result in a performance
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increase for many applications.
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</p>
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<p>
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Though most application should not notice any change (except that
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they run a little faster), if problems arise then the
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legacy behavior can be restored at compile-time by using the
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following options to the C-compiler:
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<blockquote><pre>
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-DSQLITE_DEFAULT_PAGE_SIZE=1024
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-DSQLITE_DEFAULT_CACHE_SIZE=2000
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</pre></blockquote>
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<p>
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The page size and cache size can also be set or changed at run-time using the
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<a href="pragma.html#pragma_page_size">page_size pragma</a> and <a href="pragma.html#pragma_cache_size">cache_size pragma</a>, respectively.
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<h2>3.0 Possible Negative Consequences Of This Change</h2>
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<p>
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The minimum size of an SQLite database is one page for each table and
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each index. With a larger page size, the size of an empty database
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for a given schema will grow by a factor of four, therefore. However,
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once the database begins to fill with content the size of the older
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1024-byte page databases and the newer 4096-byte page databases will
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quickly converge. Due to relaxed bin-packing constraints, the
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4096-byte page size might actually result in a smaller file, once
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substantial content is added.
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</p>
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