ch14_01.htm

By Tom Christiansen and Nathan Torkington ISBN 1-56592-243-3 First Edition, published August 1998

HREF="#ch14-pgfId-1000004415"
>5</A
>]</P
></TD
></TR
><TR
CLASS="row"
VALIGN="TOP"
><TD
CLASS="entry"
ROWSPAN="1"
COLSPAN="1"
><P
CLASS="para"
>Builds ok on Windows</P
></TD
><TD
CLASS="entry"
ROWSPAN="1"
COLSPAN="1"
><P
CLASS="para"
>N/A</P
></TD
><TD
CLASS="entry"
ROWSPAN="1"
COLSPAN="1"
><P
CLASS="para"
>yes</P
></TD
><TD
CLASS="entry"
ROWSPAN="1"
COLSPAN="1"
><P
CLASS="para"
>yes</P
></TD
><TD
CLASS="entry"
ROWSPAN="1"
COLSPAN="1"
><P
CLASS="para"
>yes[<A
CLASS="footnote"
HREF="#ch14-pgfId-1000004419"
>6</A
>]</P
></TD
></TR
><TR
CLASS="row"
VALIGN="TOP"
><TD
CLASS="entry"
ROWSPAN="1"
COLSPAN="1"
><P
CLASS="para"
>Code size</P
></TD
><TD
CLASS="entry"
ROWSPAN="1"
COLSPAN="1"
><P
CLASS="para"
>[<A
CLASS="footnote"
HREF="#ch14-pgfId-1000004432"
>7</A
>]</P
></TD
><TD
CLASS="entry"
ROWSPAN="1"
COLSPAN="1"
><P
CLASS="para"
>small</P
></TD
><TD
CLASS="entry"
ROWSPAN="1"
COLSPAN="1"
><P
CLASS="para"
>big</P
></TD
><TD
CLASS="entry"
ROWSPAN="1"
COLSPAN="1"
><P
CLASS="para"
>big[<A
CLASS="footnote"
HREF="#ch14-pgfId-1000004443"
>8</A
>]</P
></TD
></TR
><TR
CLASS="row"
VALIGN="TOP"
><TD
CLASS="entry"
ROWSPAN="1"
COLSPAN="1"
><P
CLASS="para"
>Disk usage</P
></TD
><TD
CLASS="entry"
ROWSPAN="1"
COLSPAN="1"
><P
CLASS="para"
>[<A
CLASS="footnote"
HREF="#ch14-pgfId-1000004432"
>7</A
>]</P
></TD
><TD
CLASS="entry"
ROWSPAN="1"
COLSPAN="1"
><P
CLASS="para"
>small</P
></TD
><TD
CLASS="entry"
ROWSPAN="1"
COLSPAN="1"
><P
CLASS="para"
>big</P
></TD
><TD
CLASS="entry"
ROWSPAN="1"
COLSPAN="1"
><P
CLASS="para"
>ok</P
></TD
></TR
><TR
CLASS="row"
VALIGN="TOP"
><TD
CLASS="entry"
ROWSPAN="1"
COLSPAN="1"
><P
CLASS="para"
>Speed</P
></TD
><TD
CLASS="entry"
ROWSPAN="1"
COLSPAN="1"
><P
CLASS="para"
>[<A
CLASS="footnote"
HREF="#ch14-pgfId-1000004432"
>7</A
>]</P
></TD
><TD
CLASS="entry"
ROWSPAN="1"
COLSPAN="1"
><P
CLASS="para"
>slow</P
></TD
><TD
CLASS="entry"
ROWSPAN="1"
COLSPAN="1"
><P
CLASS="para"
>ok</P
></TD
><TD
CLASS="entry"
ROWSPAN="1"
COLSPAN="1"
><P
CLASS="para"
>fast</P
></TD
></TR
><TR
CLASS="row"
VALIGN="TOP"
><TD
CLASS="entry"
ROWSPAN="1"
COLSPAN="1"
><P
CLASS="para"
>Block size limits</P
></TD
><TD
CLASS="entry"
ROWSPAN="1"
COLSPAN="1"
><P
CLASS="para"
>4k</P
></TD
><TD
CLASS="entry"
ROWSPAN="1"
COLSPAN="1"
><P
CLASS="para"
>1k[<A
CLASS="footnote"
HREF="#ch14-pgfId-1000004447"
>9</A
>]</P
></TD
><TD
CLASS="entry"
ROWSPAN="1"
COLSPAN="1"
><P
CLASS="para"
>none</P
></TD
><TD
CLASS="entry"
ROWSPAN="1"
COLSPAN="1"
><P
CLASS="para"
>none</P
></TD
></TR
><TR
CLASS="row"
VALIGN="TOP"
><TD
CLASS="entry"
ROWSPAN="1"
COLSPAN="1"
><P
CLASS="para"
>Byte-order independent</P
></TD
><TD
CLASS="entry"
ROWSPAN="1"
COLSPAN="1"
><P
CLASS="para"
>no</P
></TD
><TD
CLASS="entry"
ROWSPAN="1"
COLSPAN="1"
><P
CLASS="para"
>no</P
></TD
><TD
CLASS="entry"
ROWSPAN="1"
COLSPAN="1"
><P
CLASS="para"
>no</P
></TD
><TD
CLASS="entry"
ROWSPAN="1"
COLSPAN="1"
><P
CLASS="para"
>yes</P
></TD
></TR
><TR
CLASS="row"
VALIGN="TOP"
><TD
CLASS="entry"
ROWSPAN="1"
COLSPAN="1"
><P
CLASS="para"
>User-defined sort order</P
></TD
><TD
CLASS="entry"
ROWSPAN="1"
COLSPAN="1"
><P
CLASS="para"
>no</P
></TD
><TD
CLASS="entry"
ROWSPAN="1"
COLSPAN="1"
><P
CLASS="para"
>no</P
></TD
><TD
CLASS="entry"
ROWSPAN="1"
COLSPAN="1"
><P
CLASS="para"
>no</P
></TD
><TD
CLASS="entry"
ROWSPAN="1"
COLSPAN="1"
><P
CLASS="para"
>yes</P
></TD
></TR
><TR
CLASS="row"
VALIGN="TOP"
><TD
CLASS="entry"
ROWSPAN="1"
COLSPAN="1"
><P
CLASS="para"
>Partial key lookups</P
></TD
><TD
CLASS="entry"
ROWSPAN="1"
COLSPAN="1"
><P
CLASS="para"
>no</P
></TD
><TD
CLASS="entry"
ROWSPAN="1"
COLSPAN="1"
><P
CLASS="para"
>no</P
></TD
><TD
CLASS="entry"
ROWSPAN="1"
COLSPAN="1"
><P
CLASS="para"
>no</P
></TD
><TD
CLASS="entry"
ROWSPAN="1"
COLSPAN="1"
><P
CLASS="para"
>yes<A
CLASS="indexterm"
NAME="ch14-idx-1000004913-0"
></A
></P
></TD
></TR
></TBODY
></TABLE
><BLOCKQUOTE
CLASS="footnote"
><DIV
CLASS="footnote"
><P
CLASS="para"
><A
CLASS="footnote"
NAME="ch14-pgfId-1000004358"
>[1]</A
> Using GPLed code in your program places restrictions upon you. See <A
CLASS="systemitem.url"
HREF="http://www.gnu.org"
>www.gnu.org</A
> for more details.</P
></DIV
><DIV
CLASS="footnote"
><P
CLASS="para"
><A
CLASS="footnote"
NAME="ch14-pgfId-1000004363"
>[2]</A
> See the DB_File library method. Requires symbolic links.</P
></DIV
><DIV
CLASS="footnote"
><P
CLASS="para"
><A
CLASS="footnote"
NAME="ch14-pgfId-1000004367"
>[3]</A
> On mixed-universe machines, this may be in the BSD compatibility library, which is often shunned.</P
></DIV
><DIV
CLASS="footnote"
><P
CLASS="para"
><A
CLASS="footnote"
NAME="ch14-pgfId-1000004372"
>[4]</A
> Except for free Unix ports like Linux, FreeBSD, OpenBSD, and NetBSD.</P
></DIV
><DIV
CLASS="footnote"
><P
CLASS="para"
><A
CLASS="footnote"
NAME="ch14-pgfId-1000004415"
>[5]</A
> Providing you have an ANSI C compiler.</P
></DIV
><DIV
CLASS="footnote"
><P
CLASS="para"
><A
CLASS="footnote"
NAME="ch14-pgfId-1000004419"
>[6]</A
> Prior to unification in 5.005, several divergent versions of Perl on Windows systems were widely available, including the standard port built from the normal Perl distribution and several proprietary ports. Like most CPAN modules, DB builds only on the standard port.</P
></DIV
><DIV
CLASS="footnote"
><P
CLASS="para"
><A
CLASS="footnote"
NAME="ch14-pgfId-1000004432"
>[7]</A
> Depends on how much your vendor has tweaked it.</P
></DIV
><DIV
CLASS="footnote"
><P
CLASS="para"
><A
CLASS="footnote"
NAME="ch14-pgfId-1000004443"
>[8]</A
> Can be reduced if you compile for one access method.</P
></DIV
><DIV
CLASS="footnote"
><P
CLASS="para"
><A
CLASS="footnote"
NAME="ch14-pgfId-1000004447"
>[9]</A
> By default, but can be redefined (at the expense of compatibility with older files).</P
></DIV
></BLOCKQUOTE
><P
CLASS="para"
><A
CLASS="indexterm"
NAME="ch14-idx-1000004912-0"
></A
><A
CLASS="indexterm"
NAME="ch14-idx-1000004912-1"
></A
><A
CLASS="indexterm"
NAME="ch14-idx-1000004912-2"
></A
><A
CLASS="indexterm"
NAME="ch14-idx-1000004912-3"
></A
>NDBM comes with most BSD-derived machines. GDBM is a GNU DBM implementation. <A
CLASS="indexterm"
NAME="ch14-idx-1000004914-0"
></A
>SDBM is part of the X11 distribution and also the standard Perl source distribution. DB refers to the <A
CLASS="indexterm"
NAME="ch14-idx-1000004915-0"
></A
>Berkeley DB library. While the others are essentially reimplementations of the original DB library, the Berkeley DB code gives you three different types of database on disk and attempts to solve many of the disk, speed, and size limitations that hinder the other implementations.</P
><P
CLASS="para"
><A
CLASS="indexterm"
NAME="ch14-idx-1000004916-0"
></A
>Code size refers to the size of the compiled libraries. <A
CLASS="indexterm"
NAME="ch14-idx-1000004917-0"
></A
>Disk usage refers to the size of the database files it creates. Block size limits refer to the database's maximum key or value size. Byte-order independence refers to whether the database system relies on hardware byte order or whether it instead creates portable files. A user-defined sort order lets you tell the library what order to return lists of keys in. Partial key lookups let you make approximate searches on the database.</P
><P
CLASS="para"
>Most Perl programmers prefer the Berkeley DB implementations. Many systems already have this library installed, and Perl can use it. For others, you are advised to fetch and install it from CPAN. It will make your life much easier.</P
><P
CLASS="para"
>DBM files provide key/value pairs. In relational database terms, you get a database with one table that has only two columns. <A
CLASS="xref"
HREF="ch14_09.htm"
TITLE="Storing Complex Data in a DBM File"
>Recipe 14.8</A
> shows you how to use the <A
CLASS="indexterm"
NAME="ch14-idx-1000004918-0"
></A
>MLDBM module from CPAN to store arbitrarily complex data structures in a DBM file.</P
><P
CLASS="para"
>As good as MLDBM is, it doesn't get around the limitation that you only retrieve rows based on one single column, the hash key. If you need complex queries, the difficulties can be overwhelming. In these cases, consider a separate database management system (DBMS). The DBI project provides modules to work with Oracle, Sybase, mSQL, MySQL, Ingres, and others.</P
><P
CLASS="para"
>See <A
CLASS="systemitem.url"
HREF="http://www.hermetica.com/technologia/perl/DBI/index.html"
>http://www.hermetica.com/technologia/perl/DBI/index.html</A
> and <A
CLASS="systemitem.url"
HREF="http://www.perl.com/CPAN/modules/by-category/07_Database_Interfaces/"
>http://www.perl.com/CPAN/modules/by-category/07_Database_Interfaces/</A
>, which currently contains:</P
><PRE
CLASS="programlisting"
><CODE
CLASS="literal"
>AsciiDB   DBI Db     MLDBM    OLE    Pg        Sybase</CODE
>
<CODE
CLASS="literal"
>CDB_File  DBZ_ File  Fame     Msql   ObjStore  Postgres  XBase</CODE
>
<CODE
CLASS="literal"
>DBD       DB_File    Ingperl  MySQL  Oraperl   Sprite</CODE
></PRE
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