BlitzNG
/
database.mod
-ын хуулбар https://github.com/bmx-ng/database.mod.git


			
							123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122
							<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
<html><head>
<title>In-Memory Databases</title>
<style type="text/css">
body {
    margin: auto;
    font-family: Verdana, sans-serif;
    padding: 8px 1%;
}

a { color: #45735f }
a:visited { color: #734559 }

.logo { position:absolute; margin:3px; }
.tagline {
  float:right;
  text-align:right;
  font-style:italic;
  width:240px;
  margin:12px;
  margin-top:58px;
}

.toolbar {
  font-variant: small-caps;
  text-align: center;
  line-height: 1.6em;
  margin: 0;
  padding:1px 8px;
}
.toolbar a { color: white; text-decoration: none; padding: 6px 12px; }
.toolbar a:visited { color: white; }
.toolbar a:hover { color: #80a796; background: white; }

.content    { margin: 5%; }
.content dt { font-weight:bold; }
.content dd { margin-bottom: 25px; margin-left:20%; }
.content ul { padding:0px; padding-left: 15px; margin:0px; }

/* rounded corners */
.se  { background: url(images/se.png) 100% 100% no-repeat #80a796}
.sw  { background: url(images/sw.png) 0% 100% no-repeat }
.ne  { background: url(images/ne.png) 100% 0% no-repeat }
.nw  { background: url(images/nw.png) 0% 0% no-repeat }

</style>
<meta http-equiv="content-type" content="text/html; charset=UTF-8">
  
</head>
<body>
<div><!-- container div to satisfy validator -->


<h1 align="center">In-Memory Databases</h1>

<p>An SQLite database is normally stored in a single ordinary disk
file. However, in certain circumstances, the database might be stored in
memory.</p>

<p>The most common way to force an SQLite database to exist purely 
in memory is to open the database using the special filename
"<b>:memory:</b>".  In other words, instead of passing the name of
a real disk file into the LoadDatase function, pass in the string ":memory:".  For
example:</p>

<blockquote><pre>
rc = sqlite3_open(":memory:", &db);
</pre></blockquote>

<p>When this is done, no disk file is opened.  
Instead, a new database is created
purely in memory.  The database ceases to exist as soon as the database
connection is closed.  Every :memory: database is distinct from every
other.  So, opening two database connections each with the filename
":memory:" will create two independent in-memory databases.</p>

<p>The special filename ":memory:" can be used anywhere that a database
filename is permitted.  For example, it can be used as the
<i>filename</i> in an <a href="lang_attach.html">ATTACH</a> command:</p>

<blockquote>
<b>ATTACH DATABASE ':memory:' AS aux1;</b>
</blockquote>

<p>Note that in order for the special ":memory:" name to apply and to
create a pure in-memory database, there must be no additional text in the
filename.  Thus, a disk-based database can be created in a file by prepending
a pathname, like this:  "./:memory:".</p>

<a name="temp_db"></a>

<h2>Temporary Databases</h2>

<p>When the name of the database file handed to LoadDatabase() or to
<a href="lang_attach.html">ATTACH</a> is an empty string, then a new temporary file is created to hold
the database.</p>

<blockquote><pre>
rc = sqlite3_open("", &db);
</pre></blockquote>

<blockquote><b>
ATTACH DATABASE '' AS aux2;
</b></blockquote>

<p>A different temporary file is created each time, so that just like as
with the special ":memory:" string, two database connections to temporary
databases each have their own private database.  Temporary databases are
automatically deleted when the connection that created them closes.</p>

<p>Even though a disk file is allocated for each temporary database, in
practice the temporary database usually resides in the in-memory pager
cache and hence is very little difference between a pure in-memory database
created by ":memory:" and a temporary database created by an empty filename.
The sole difference is that a ":memory:" database must remain in memory
at all times whereas parts of a temporary database might be flushed to
disk if database becomes large or if SQLite comes under memory pressure.</p>

<p>The previous paragraphs describe the behavior of temporary databases
under the default SQLite configuration.  
</p>