Adding upstream version 3.40.1.upstream/3.40.1 upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
author: Daniel Baumann <daniel.baumann@progress-linux.org> 2024-05-05 17:28:19 +0000
committer: Daniel Baumann <daniel.baumann@progress-linux.org> 2024-05-05 17:28:19 +0000
commit: 18657a960e125336f704ea058e25c27bd3900dcb (patch)
tree: 17b438b680ed45a996d7b59951e6aa34023783f2 /www/imposter.html
parent: Initial commit. (diff)
download: sqlite3-18657a960e125336f704ea058e25c27bd3900dcb.tar.xz
sqlite3-18657a960e125336f704ea058e25c27bd3900dcb.zip
1 files changed, 351 insertions, 0 deletions
diff --git a/www/imposter.html b/www/imposter.html
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+<!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>Imposter Tables</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>
+<div class=fancy>
+<div class=nosearch>
+<div class="fancy_title">
+Imposter Tables
+</div>
+</div>
+
+
+
+
+<h1 id="introduction"><span>1. </span>Introduction</h1>
+
+<p>
+An imposter table is a table that is attached to the same <a href="fileformat2.html#btree">b-tree</a>
+as an index.
+An imposter table allows the content of an index to be queried or
+modified as if the index were an ordinary table.
+</p>
+
+<p>
+Imposter tables are intended for analysis and debugging only.
+This is not a feature that most application developers should understand
+or even know about.
+Imposter tables are for experts only.
+</p>
+
+<p>
+Improper use of imposter tables can cause index corruption, though
+any corruption created this way can be fixed by running <a href="lang_reindex.html">REINDEX</a>.
+</p>
+
+<h1 id="details"><span>2. </span>Details</h1>
+
+<p>
+Each table and each index in SQLite is stored in a separate b-tree
+in the database file.  Each b-tree is identified by its root page
+number.  The root page number for any index or table can be found
+by querying the "rootpage" column of the <a href="schematab.html">sqlite_schema table</a>.
+See the <a href="queryplanner.html">indexing tutorial</a> and the <a href="fileformat2.html">file format</a> documentation
+for further background on this design.
+</p>
+
+<p>
+Usually the b-trees for tables and indexes are slightly different.
+A table b-tree contains a 64-bit integer key and arbitrary data.
+The 64-bit integer key is the <a href="lang_createtable.html#rowid">ROWID</a>.  Index b-trees contain
+an arbitrary binary key and no data.  So table b-trees and index
+b-trees are not directly compatible.
+</p>
+
+<p>
+However, the b-tree for a <a href="withoutrowid.html">WITHOUT ROWID</a> table is in the same format
+as an index b-tree.  Thus, an index b-tree can be accessed as if it
+were a WITHOUT ROWID table.
+</p>
+
+<h2 id="manually_created_imposter_tables"><span>2.1. </span>Manually Created Imposter Tables</h2>
+
+<p>
+One way to create an imposter table is to directly edit the sqlite_schema
+table to insert a new row that describes the table.
+For example, suppose the schema is like this:
+</p>
+
+<div class="codeblock"><pre>CREATE TABLE t1(a INTEGER PRIMARY KEY,b TEXT,c INT, d INT);
+CREATE INDEX t1bc ON t1(b,c);
+</pre></div>
+
+<p>
+The WITHOUT ROWID table that has the same structure as the t1bc index
+would look like this:
+</p>
+
+<div class="codeblock"><pre>CREATE TABLE t2(b TEXT,c INT,a INT, PRIMARY KEY(b,c,a)) WITHOUT ROWID;
+</pre></div>
+
+<p>
+To create a permanent imposter table "t2" against index "t1bc" one
+should first enable editing of the sqlite_schema table by running
+"<a href="pragma.html#pragma_writable_schema">PRAGMA writable_schema=ON</a>".
+(Be careful to observe the warnings that accompany this PRAGMA.
+A mistake can cause severe database corruption.)
+Then insert a new entry into the sqlite_schema table like this:
+</p>
+
+<div class="codeblock"><pre>INSERT INTO sqlite_schema(type,name,tbl_name,rootpage,sql)
+ SELECT 'table','t2','t2',rootpage,
+   'CREATE TABLE t2(b,c,a,PRIMARY KEY(b,c,a))WITHOUT ROWID'
+   FROM sqlite_schema
+  WHERE name='t1bc';
+</pre></div>
+
+<p>
+The INSERT statement above adds a new row to the sqlite_schema table that
+defines a table "t2" having the same on-disk format as index "t1bc" and 
+pointing to the same b-tree.
+After adding this sqlite_schema table entry, it is necessary to close and
+reopen the database in order to get SQLite to reread the schema.
+Then the "t2" table can be queried to see the content of the "t1bc" index.
+</p>
+
+<h3 id="corrupted_database"><span>2.1.1. </span>Corrupted Database</h3>
+
+<p>
+A serious problem with the manual imposter table approach described above
+is that after adding the new "t2" entry to the "sqlite_schema" table, the
+database file will technically be corrupt.  Both the "t1bc" index and the
+"t2" table will point to the same b-tree.  This will not cause
+any immediate problems, though one should avoid running <a href="lang_vacuum.html">VACUUM</a>.
+</p>
+
+<p>
+It is possible to write into the "t2" table, thus changing the content
+of the index.
+But doing so will get the "t1bc" index out of synchronization with its
+parent table "t1".  An out-of-sync index can result in incorrect query
+results.
+</p>
+
+<p>
+Since the "t2" imposter table is a form of database corruption, the
+manual approach to creating imposter tables is not recommended.
+Actually, any use of imposter tables is discouraged for all but
+expert developers, but manually created imposter tables are
+especially discouraged because they are permanent.
+</p>
+
+<h2 id="transient_imposter_tables"><span>2.2. </span>Transient Imposter Tables</h2>
+
+<p>
+Another (safer) approach to creating an imposter table is to add an
+entry for the imposter table to SQLite's internal symbol table without
+updating the "sqlite_schema" table on disk.
+That way, the imposter table exists in only a single database connection
+and is automatically removed whenever the schema is reloaded.
+</p>
+
+<p>
+Creation of a transient imposter table involves a special
+<a href="c3ref/test_control.html">sqlite3_test_control()</a> call.  Unlike all other SQLite APIs,
+<a href="c3ref/test_control.html">sqlite3_test_control()</a> interface is subject to incompatible changes
+from one release to the next, and so the mechanism described below
+is not guaranteed to work in future releases of SQLite.  The
+SQLite developers do not consider this a problem because imposter
+tables should not be used in applications.  Imposter tables are for
+analysis and testing use only.
+</p>
+
+<p>
+To create a transient imposter table, first call sqlite3_test_control()
+as follows:
+</p>
+
+<div class="codeblock"><pre>sqlite3_test_control(SQLITE_TESTCTRL_IMPOSTER, db, "main", 1, tnum);
+</pre></div>
+
+<p>
+The "db" parameter is a pointer to the <a href="c3ref/sqlite3.html">database connection</a>.
+The "main" argument is the name of the schema in which the imposter
+table is to be created.  The "1" argument enables the imposter table
+mechanism.  "tnum" is the root page of the index that the imposter
+table should mirror.
+</p>
+
+<p>
+After the sqlite3_test_control() call above, then run a <a href="lang_createtable.html">CREATE TABLE</a>
+statement the defines the imposter table.
+With the imposter mechanism enabled, this CREATE TABLE statement does
+not create a real table but instead merely adds an entry in SQLite's
+internal symbol table.  Note that the CREATE TABLE statement must
+be in the correct format for the index.  If the imposter table has the
+wrong number of columns or is not a <a href="withoutrowid.html">WITHOUT ROWID</a> table or is otherwise
+incompatible with the index b-tree, then <a href="rescode.html#corrupt">SQLITE_CORRUPT</a> errors will result
+when the imposter table is used.
+</p>
+
+<p>
+After running the CREATE TABLE statement, disable the imposter mechanism
+as follows:
+</p>
+
+<div class="codeblock"><pre>sqlite3_test_control(SQLITE_TESTCTRL_IMPOSTER, db, "main", 0, 0);
+</pre></div>
+
+<p>
+In other words, make the same sqlite3_test_control() call except change
+the last two parameters to zero.
+</p>
+
+<p>
+After the imposter table is loaded into SQLite's internal schema as
+described above, the imposter table can be used as any other table.
+But the imposter table will only be visible to the one database
+connection that created it.  No changes are made to the database file
+on disk.  And the imposter table will disappear the next time the schema 
+is loaded.
+</p>
+
+<a name="dotimposter"></a>
+
+<h2 id="the_imposter_shell_command"><span>2.3. </span>The .imposter Shell Command</h2>
+
+<p>
+As of SQLite 3.16.0 (2017-01-02), the <a href="cli.html">command-line shell</a> contains
+a dot-command ".imposter" that does all of the work of setting up a
+transient imposter table.
+Instead of making multiple calls to sqlite3_test_control() and figuring
+out and invoking a compatible CREATE TABLE statement, a transient
+imposter table can be constructed as follows:
+</p>
+
+<div class="codeblock"><pre>.imposter t1bc t2
+</pre></div>
+
+<p>
+Of course, substitute the desired index and imposter table names in
+place of the "t1bc" and "t2" shown in the example.
+The ".imposter" command reads the schema of the "t1bc" index, uses
+that information to construct a compatible CREATE TABLE statement for
+the imposter table, then makes all the necessary calls to create the
+transient imposter table automatically.
+</p>
+
+<h1 id="summary_and_final_warning"><span>3. </span>Summary And Final Warning</h1>
+
+<p>
+The imposter table mechanism is a power analysis and debugging tool
+for SQLite.  But as with all sharp tools, it can also be dangerous and
+can result in corrupt database files if misused.  Do not attempt to
+use imposter tables in an application.  Imposter tables are intended
+for use in the laboratory by experts.
+</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/imposter.in?m=219fd65ee2ac4eadd">2020-06-18 21:18:56</a> UTC </small></i></p>
+
author	Daniel Baumann <daniel.baumann@progress-linux.org>	2024-05-05 17:28:19 +0000
committer	Daniel Baumann <daniel.baumann@progress-linux.org>	2024-05-05 17:28:19 +0000
commit	18657a960e125336f704ea058e25c27bd3900dcb (patch)
tree	17b438b680ed45a996d7b59951e6aa34023783f2 /www/imposter.html
parent	Initial commit. (diff)
download	sqlite3-18657a960e125336f704ea058e25c27bd3900dcb.tar.xz sqlite3-18657a960e125336f704ea058e25c27bd3900dcb.zip