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191 lines
8.3 KiB
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<!--Copyright 1999-2002 by Sleepycat Software, Inc.-->
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<HTML>
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<META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859-1">
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<META NAME="GENERATOR" CONTENT="Mozilla/4.08 [en] (X11; I; FreeBSD 2.2.8-19990120-SNAP i386) [Netscape]">
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</HEAD>
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<BODY>
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<H2>
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<A NAME="Memory Pool Commands"></A>Memory Pool Commands</H2>
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Memory pools are used in a manner similar to the other subsystems.
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We create a handle to the pool and then use it for a variety of operations.
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Some of the memory pool commands use the environment instead. Those are
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presented first.
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<P><B>> <env> mpool_stat</B>
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<P>This command returns the statistics associated with the memory
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pool subsystem. It is a direct call to the <A HREF="../../docs/api_c/memp_stat.html">memp_stat</A>
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function. It returns a list of name/value pairs of the DB_MPOOL_STAT
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structure.
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<BR>
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<HR WIDTH="100%">
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<BR><B>> <env> mpool_sync <I>lsn</I></B>
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<P>This command flushes the memory pool for all pages with a log sequence
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number less than <B><I>lsn</I></B>. It is a direct call to the <A HREF="../../docs/api_c/memp_sync.html">memp_sync </A>
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function. It returns either a 0 (for success), a DB error message
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or it throws a Tcl error with a system message.
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<BR>
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<HR WIDTH="100%">
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<BR><B>> <env> mpool_trickle <I>percent</I></B>
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<P>This command tells DB to ensure that at least <B><I>percent</I></B>
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percent of the pages are clean by writing out enough to dirty pages to
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achieve that percentage. It is a direct call to the <A HREF="../../docs/api_c/memp_trickle.html">memp_trickle</A>
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function. The command will return the number of pages actually written.
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It returns either the number of pages on success, or it throws a Tcl error
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with a system message.
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<BR>
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<HR WIDTH="100%">
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<P><B>> <env> mpool [-create] [-nommap] [-rdonly] [-mode <I>mode</I>]
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-pagesize <I>size</I> [<I>file</I>]</B>
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<P>This command creates a new memory pool. It invokes the <A HREF="../../docs/api_c/memp_fopen.html">memp_fopen</A>
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function. After it successfully gets a handle to a memory pool, we
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bind it to a new Tcl command of the form <B><I>$env.mpX</I></B>, where
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X is an integer starting at 0 (e.g. <B>$env.mp0, $env.mp1, </B>etc).
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We use the <I>Tcl_CreateObjCommand()</I> to create the top level memory
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pool functions. It is through this handle that the user can manipulate
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the pool. Internally, the handle we get back from DB will be stored
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as the <I>ClientData</I> portion of the new command set so that future
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memory pool calls will have that handle readily available. Additionally,
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we need to maintain this handle in relation to the environment so that
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if the user calls <A HREF="../../docs/api_tcl/env_close.html"><env> close</A> without closing
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the memory pool we can properly clean up. The arguments are:
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<UL>
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<LI>
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<B><I>file</I></B> is the name of the file to open</LI>
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<LI>
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<B>-create </B>selects the DB_CREATE flag to create underlying file</LI>
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<LI>
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<B>-mode <I>mode </I></B>sets the permissions of created file to <B><I>mode</I></B></LI>
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<LI>
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<B>-nommap</B> selects the DB_NOMMAP flag to disallow using mmap'ed files</LI>
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<LI>
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<B>-pagesize</B> sets the underlying file page size to <B><I>size</I></B></LI>
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<LI>
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<B>-rdonly </B>selects the DB_RDONLY flag for read only access</LI>
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</UL>
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<HR WIDTH="100%">
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<BR><B>> <mp> close</B>
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<P>This command closes the memory pool. It is a direct call to the
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<A HREF="../../docs/api_c/memp_fclose.html">memp_close</A>
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function. It returns either a 0 (for success), a DB error message
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or it throws a Tcl error with a system message.
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<P>Additionally, since the handle is no longer valid, we will call
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<I>Tcl_DeleteCommand()
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</I>so
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that further uses of the handle will be dealt with properly by Tcl itself.
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We must also remove the reference to this handle from the environment.
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We will go through the list of pinned pages that were acquired by the <A HREF="#> <mp> get">get</A>
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command and
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<A HREF="#> <pg> put">put</A> them back.
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<HR WIDTH="100%">
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<BR><B>> <mp> fsync</B>
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<P>This command flushes all of the file's dirty pages to disk. It
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is a direct call to the <A HREF="../../docs/api_c/memp_fsync.html">memp_fsync</A>
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function. It returns either a 0 (for success), a DB error message
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or it throws a Tcl error with a system message.
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<HR WIDTH="100%">
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<BR><A NAME="> <mp> get"></A><B>> <mp> get [-create] [-last] [-new]
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[<I>pgno</I>]</B>
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<P>This command gets the <B><I>pgno </I></B>page from the memory
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pool. It invokes the <A HREF="../../docs/api_c/memp_fget.html">memp_fget</A>
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function and possibly the <A HREF="../../docs/api_c/memp_fset.html">memp_fset</A>
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function if any options are chosen to set the page characteristics.
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After it successfully gets a handle to a page, we bind it to and
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return a new Tcl command of the form <B><I>$env.mpN.pX</I></B>, where X
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is an integer starting at 0 (e.g. <B>$env.mp0.p0, $env.mp1.p0, </B>etc).
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We use the <I>Tcl_CreateObjCommand()</I> to create the top level page functions.
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It is through this handle that the user can manipulate the page.
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Internally, the handle we get back from DB will be stored as the <I>ClientData</I>
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portion of the new command set. We need to store this handle in
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relation to the memory pool handle so that if the memory pool is closed,
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we will <A HREF="#> <pg> put">put</A> back the pages (setting the discard
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flag) and delete that set of commands.
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<P>The arguments are:
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<UL>
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<LI>
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<B>-create </B>selects the DB_MPOOL_CREATE flag to create the page
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if it does not exist.</LI>
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<LI>
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<B>-last</B> selects the DB_MPOOL_LAST flag to return the last page in
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the file</LI>
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<LI>
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<B>-new</B> selects the DB_MPOOL_NEW flag to create a new page</LI>
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</UL>
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<HR WIDTH="100%">
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<BR><B>> <pg> pgnum</B>
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<P>This command returns the page number associated with this memory pool
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page. Primarily it will be used after an <A HREF="#> <mp> get"><mp>
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get</A> call.
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<BR>
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<HR WIDTH="100%"><B>> <pg> pgsize</B>
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<P>This command returns the page size associated with this memory pool
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page. Primarily it will be used after an <A HREF="#> <mp> get"><mp>
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get</A> call.
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<BR>
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<HR WIDTH="100%"><B>> <pg> set [-clean] [-dirty] [-discard]</B>
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<P>This command sets the characteristics of the page. It is a direct
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call to the <A HREF="../../docs/api_c/memp_fset.html">memp_fset</A> function.
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It returns either a 0 (for success), a DB error message or it throws a
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Tcl error with a system message. The arguments are:
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<UL>
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<LI>
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<B>-clean</B> selects the DB_MPOOL_CLEAN flag to indicate this is a clean
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page</LI>
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<LI>
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<B>-dirty</B> selects the DB_MPOOL_DIRTY flag to indicate this page should
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be flushed before eviction</LI>
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<LI>
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<B>-discard</B> selects the DB_MPOOL_DISCARD flag to indicate this page
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is unimportant</LI>
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</UL>
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<HR WIDTH="100%">
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<BR><A NAME="> <pg> put"></A><B>> <pg> put [-clean] [-dirty] [-discard]</B>
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<P>This command will put back the page to the memory pool. It is
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a direct call to the <A HREF="../../docs/api_c/memp_fput.html">memp_fput</A>
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function. It returns either a 0 (for success), a DB error message
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or it throws a Tcl error with a system message. Additionally, since the
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handle is no longer valid, we will call
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<I>Tcl_DeleteCommand()
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</I>so that
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further uses of the handle will be dealt with properly by Tcl itself.
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We must also remove the reference to this handle from the memory pool.
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<P>The arguments are:
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<UL>
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<LI>
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<B>-clean</B> selects the DB_MPOOL_CLEAN flag to indicate this is a clean
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page</LI>
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<LI>
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<B>-dirty</B> selects the DB_MPOOL_DIRTY flag to indicate this page should
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be flushed before eviction</LI>
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<LI>
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<B>-discard</B> selects the DB_MPOOL_DISCARD flag to indicate this page
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is unimportant</LI>
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</UL>
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<HR WIDTH="100%">
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<BR><B>> <pg> init <I>val|string</I></B>
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<P>This command initializes the page to the <B><I>val</I></B> given or
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places the <B><I>string</I></B> given at the beginning of the page.
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It returns a 0 for success or it throws a Tcl error with an error message.
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<P>
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<HR WIDTH="100%">
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<BR><B>> <pg> is_setto <I>val|string</I></B>
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<P>This command verifies the page contains the <B><I>val</I></B> given
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or checks that the <B>string</B> given is at the beginning of the page.
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It returns a 1 if the page is correctly set to the value and a 0 otherwise.
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