Problem:
I've come across a small niggle in the sqlite web pages' html tree,
which may or may not be important, it certainly isn't urgent, but not my
place to judge what is important and what not, so posting it anyway.
(Details pasted at the bottom of this mail if it merits further looking
into.)
Description:
There is a innocuous but persistent occurrence in the website source
HTML pages where it emits an unopened extra closing tag (</div> to be
precise). It's near everywhere (everywhere I've checked, but my checking
was not exhaustive) and in consistent relative placement, which leads me
to believe the problem to be programmatic or due to a template.
I found this making a parser for web documents (so it can be reformatted
to a more compact view) to use in an SQLite manager utility. Now both
my parser and any other modern browser will swallow the dangling tag
without complaint, which is why it is innocuous. I guess the worst
problem is the slight tickle of an OCD nerve. :)
That said, perhaps it is of interest.
Detail:
This example for the ...sqlite.org/lang_analyze.html (chosen for having
relatively little html code, but any page could have been chosen).
Problem occurs on line 93 in this file, always after the closing tag of
the script section (See highlight):
Alternatively, open in modern browser, then open the "View page source"
- it should be nicely highlighted (Firefox, for instance, marks it red).
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd";><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>SQLite Query Language:
ANALYZE</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.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; } </script>*############# This
is the dangling tag -->* </div><div class=nosearch><h1
align="center">SQL As Understood By SQLite</h1><p><a
href="lang.html">[Top]</a></p><h2>ANALYZE</h2></div><p><b><a
href="syntax/analyze-stmt.html">analyze-stmt:</a></b><button id='x829'
onclick='hideorshow("x829","x830")'>hide</button></p><div id='x830'
class='imgcontainer'><img alt="syntax diagram analyze-stmt"
src="images/syntax/analyze-stmt.gif" /></div><p>The ANALYZE command
gathers statistics about tables and indices and stores the collected
information in <a href="fileformat2.html#intschema">internal
tables</a>of the database where the query optimizer can access the
information and use it to help make better query planning choices. If no
arguments are given, all attached databases are analyzed. If a schema
name is given as the argument, then all tables and indices in that one
database are analyzed. If the argument is a table name, then only that
table and the indices associated with that table are analyzed. If the
argument is an index name, then only that one index is
analyzed.</p><p>The default implementation stores all statistics in a
single table named "<a
href="fileformat2.html#stat1tab">sqlite_stat1</a>". If SQLite is
compiled with the <a
href="compile.html#enable_stat3">SQLITE_ENABLE_STAT3</a>option and
without the <a
href="compile.html#enable_stat4">SQLITE_ENABLE_STAT4</a>option, then
additional histogram data is collected and stored in <a
href="fileformat2.html#stat3tab">sqlite_stat3</a>. If SQLite is compiled
with the <a
href="compile.html#enable_stat4">SQLITE_ENABLE_STAT4</a>option, then
additional histogram data is collected and stored in <a
href="fileformat2.html#stat4tab">sqlite_stat4</a>. Older versions of
SQLite would make use of the <a
href="fileformat2.html#stat2tab">sqlite_stat2</a>table when compiled
with <a href="compile.html#enable_stat2">SQLITE_ENABLE_STAT2</a>but all
recent versions of SQLite ignore the sqlite_stat2 table. Future
enhancements may create additional <a
href="fileformat2.html#intschema">internal tables</a>with the same name
pattern except with final digit larger than "4". All of these tables are
collectively referred to as "statistics tables". </p><p>The content of
the statistics tables can be queried using <a
href="lang_select.html">SELECT</a>and can be changed using the <a
href="lang_delete.html">DELETE</a>, <a
href="lang_insert.html">INSERT</a>, and <a
href="lang_update.html">UPDATE</a>commands. The <a
href="lang_droptable.html">DROP TABLE</a>command works on statistics
tables as of SQLite version 3.7.9. (2011-11-01) The <a
href="lang_altertable.html">ALTER TABLE</a>command does not work on
statistics tables. Appropriate care should be used when changing the
content of the statistics tables as invalid content can cause SQLite to
select inefficient query plans. Generally speaking, one should not
modify the content of the statistics tables by any mechanism other than
invoking the ANALYZE command. See "<a
href="optoverview.html#manctrl">Manual Control Of Query Plans Using
SQLITE_STAT Tables</a>" for further information.</p><p>Statistics
gathered by ANALYZE are not automatically updated as the content of the
database changes. If the content of the database changes significantly,
or if the database schema changes, then one should consider rerunning
the ANALYZE command in order to update the statistics.</p><p>The query
planner loads the content of the statistics tables into memory when the
schema is read. Hence, when an application changes the statistics tables
directly, SQLite will not immediately notice the changes. An application
can force the query planner to reread the statistics tables by running
<b>ANALYZE sqlite_master</b>. </p><a
name="autoanalyze"></a><h2>Automatically Running ANALYZE</h2><p>The <a
href="pragma.html#pragma_optimize">PRAGMA optimize</a>command will
automatically run ANALYZE on individual tables on an as-needed basis.
The recommended practice is for applications to invoke the <a
href="pragma.html#pragma_optimize">PRAGMA optimize</a>statement just
before closing each database connection.</p><p>Each SQLite <a
href="c3ref/sqlite3.html">database connection</a>records cases when the
query planner would benefit from having accurate results of ANALYZE at
hand. These records are held in memory and accumulate over the life of a
database connection. The <a href="pragma.html#pragma_optimize">PRAGMA
optimize</a>command looks at those records and runs ANALYZE on only
those tables for which new or updated ANALYZE data seems likely to be
useful. In most cases <a href="pragma.html#pragma_optimize">PRAGMA
optimize</a>will not run ANALYZE, but it will occasionally do so either
for tables that have never before been analyzed, or for tables that have
grown significantly since they were last analyzed.</p><p>Since the
actions of <a href="pragma.html#pragma_optimize">PRAGMA optimize</a>are
determined to some extent by prior queries that have been evaluated on
the same database connection, it is recommended that <a
href="pragma.html#pragma_optimize">PRAGMA optimize</a>be deferred until
the database connection is closing and has thus had an opportunity to
accumulate as must usage information as possible. It is also reasonable
to set a timer to run <a href="pragma.html#pragma_optimize">PRAGMA
optimize</a>every few hours, or every few days, for database connections
that stay open for a long time.</p><p>Applications that desire more
control can run <a href="pragma.html#pragma_optimize">PRAGMA
optimize(0x03)</a>to obtain a list of ANALYZE commands that SQLite
thinks are appropriate to run, but without actually running those
commands. If the returned set is non-empty, the application can then
make a decision about whether or not to run the suggested ANALYZE
commands, perhaps after prompting the user for guidance.</p><p>The <a
href="pragma.html#pragma_optimize">PRAGMA optimize</a>command was first
introduced with SQLite 3.18.0 (2017-03-28) and is a no-op for all prior
releases of SQLite.</p><h2>Anticipated Future Enhancements</h2><p>All
existing versions of SQLite do a full table scan for ANALYZE. This can
be slow for multi-gigabyte and larger databases. Future versions of
SQLite might use random sampling rather than a full table scan to obtain
estimates for the database shape, especially on larger tables. The
results would approximate, but will be close enough for query planning
purposes. As of 2017-03-20, this concept has been tested in experimental
branches and appears to work well, but has not been folded into an
official release.</p>
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