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diff --git a/www/c3ref/autovacuum_pages.html b/www/c3ref/autovacuum_pages.html new file mode 100644 index 0000000..13a81da --- /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. 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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 canceled. 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="../c3ref/objlist.html">Objects</a>, + <a href="../c3ref/constlist.html">Constants</a>, and + <a href="../c3ref/funclist.html">Functions</a>.</p> + |