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diff --git a/www/shortnames.html b/www/shortnames.html new file mode 100644 index 0000000..2fd104f --- /dev/null +++ b/www/shortnames.html @@ -0,0 +1,241 @@ +<!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>8+3 Filenames</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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But on systems that impose 8+3 filename +constraints, the auxiliary files do not fit the 8+3 format even though +the original database file does. +</p> + + +<h2>Changing Filesystems</h2> + +<p> +The recommended fix for this problem is to select a different +filesystem. These days, there is a huge selection of high-performance, +reliable, patent-free filesystems that support long filenames. +Where possible, it is recommended that embedded devices use one +of these other filesystems. This will avoid compatibility issues +and the danger of +<a href="shortnames.html#db83corrupt">database corruption caused by inconsistent use of 8+3 filenames</a>. +</p> + +<h2>Adjusting SQLite To Use 8+3 Filenames</h2> + +<p> +Some devices are compelled to use an older filesystem with 8+3 +filename restrictions for backwards compatibility, or due +to other non-technical factors. In such situations, SQLite can be +coerced into using auxiliary files that fit the 8+3 pattern as follows: +</p> + +<ol> +<li><p>Compile the SQLite library with the either the compile-time + options <a href="compile.html#enable_8_3_names">SQLITE_ENABLE_8_3_NAMES=1</a> or + <a href="compile.html#enable_8_3_names">SQLITE_ENABLE_8_3_NAMES=2</a>. + Support for 8+3 filenames is not included in SQLite by default + because it does introduce some overhead. The overhead is tiny, + but even so, we do not want to burden the billions of SQLite + applications that do not need 8+3 filename support.</p> + +<li><p>If the <a href="compile.html#enable_8_3_names">SQLITE_ENABLE_8_3_NAMES=1</a> option + is used, then SQLite is capable of using 8+3 filenames but that + capabilities is disabled and must be enabled separately for each + database connection by using + using <a href="uri.html">URI filenames</a> when <a href="c3ref/open.html">opening</a> or + <a href="lang_attach.html">ATTACH-ing</a> the database files and include the + "<tt>8_3_names=1</tt>" query parameter in the URI. If SQLite + is compiled with + <a href="compile.html#enable_8_3_names">SQLITE_ENABLE_8_3_NAMES=2</a> then + 8+3 filenames are enabled by default and this step can be + skipped.</p> + +<li><p>Make sure that database filenames follow the 8+3 filename + format and that they do not have an empty name or extension. + In other words, the database filename must contain between + 1 and 8 characters in the base name and between 1 and 3 characters + in the extension. Blank extensions are not allowed.</p> +</ol> + +<p> +When the steps above are used, SQLite will shorten filename extensions +by only using the last 3 characters of +the extension. Thus, for example, a file that would normally be called +"<tt>app.db-journal</tt>" is shortened to just "<tt>app.nal</tt>". +Similarly, "<tt>app.db-wal</tt>" will become "<tt>app.wal</tt>" and +"<tt>app.db-shm</tt>" becomes "<tt>app.shm</tt>". +</p> + +<p> +Note that it is very important that the database filename have some kind +of extension. If there is no extension, then SQLite creates auxiliary +filenames by appending to the base name of the file. Thus, a database +named "<tt>db01</tt>" would have a <a href="lockingv3.html#rollback">rollback journal</a> file named +"<tt>db01-journal</tt>". And as this filename has no extension to shorten +to 3 characters, it will be used as-is, and will violate 8+3 naming rules. +</p> + +<a name="db83corrupt"></a> + +<h2>Database Corruption Warning</h2> + +<p> +If a database file is accessed using 8+3 naming rather than the default +long filename, then it must be consistently accessed +using 8+3 naming by every database +connection every time it is opened, or else there is a risk of database +corruption. +The auxiliary <a href="lockingv3.html#rollback">rollback journal</a> and <a href="wal.html">write-ahead log</a> files are essential +to SQLite for being about to recover from a crash. If an application is +using 8+3 names and crashes, then the information needed to safely recover +from the crash is stored in files with the "<tt>.nal</tt>" or +"<tt>.wal</tt>" extension. If the next application to open the database +does not specify the "<tt>8_3_names=1</tt>" URI parameter, then SQLite +will use the long filenames to try to locate the rollback journal or +write-ahead log files. It will not find them, since they were saved using +8+3 names by the application that crashed, and hence the database will not +be properly recovered and will likely go corrupt. +</p> + +<p> +Using a database file with 8+3 filenames in some cases while in +other cases using long filenames is equivalent to +<a href="howtocorrupt.html#delhotjrnl">deleting a hot journal</a>. +</p> +<p align="center"><small><i>This page last modified on <a href="https://sqlite.org/docsrc/honeypot" id="mtimelink" data-href="https://sqlite.org/docsrc/finfo/pages/shortnames.in?m=7fc7e0cffc">2022-01-08 05:02:57</a> UTC </small></i></p> + |