I've been using PostgreSQL for years, and I've often made use of cacheing of functions.

Last year I discovered - working on an Oracle 10g environment, that any sort of caching of functinon results does not exist.  (It does for 11, though)  This totally blew me away, and lead to the following soluction.  PostgreSQL people may enjoy reading what they can happily avoid... 

The solution utilises oracle Packages.  These are assembles of functions and procedures that stay in memory for a time after first being called.  The packages can contain member private variables - and these are what we use to cache the results.

The result of doing this calculation in a cached function was a halving of run-time.

CREATE OR REPLACE PACKAGE         SCHEMA.etl_utils IS
       FUNCTION cache_clear RETURN INTEGER;
       FUNCTION keyword_text_clean(i_rawtext IN VARCHAR2 ) RETURN VARCHAR2;
END etl_utils;

create or replace PACKAGE BODY         SCHEMA.etl_utils IS
    TYPE assoc_array_str_type IS TABLE OF VARCHAR2(200) INDEX BY VARCHAR2(200);
    TYPE array_num_type IS TABLE OF number INDEX BY pls_integer;   
    TYPE assoc_array_nums_type IS TABLE OF array_num_type INDEX BY VARCHAR2(200);
   
    assoc_array_str assoc_array_str_type;
   
    assoc_array_nums assoc_array_nums_type;

    FUNCTION cache_clear RETURN INTEGER
    AS
    BEGIN
         assoc_array_str.DELETE;
         assoc_array_nums.DELETE;
         RETURN 1;
    END;

    FUNCTION keyword_text_clean(i_rawtext IN VARCHAR2 ) RETURN VARCHAR2
    AS
      l_out VARCHAR2(200);
      l_out_upper VARCHAR2(200);
      l_key VARCHAR2(200);
      l_found BOOLEAN := TRUE; -- set to TRUE to enable caching
    BEGIN
        l_key := trim(i_rawtext);
        BEGIN
              l_out := assoc_array_str( l_key );
        EXCEPTION
                WHEN OTHERS THEN
                     l_found := FALSE;
         END;

         --sometimes short text comes back NULL erroneously
         --this means we can't rely on looking up the keys that should resovle to null
         --pain but makes only a small difference
         IF l_out IS NULL THEN
                  l_found := FALSE;
         END IF;

--do calculation for value and store in array-cache.
         IF NOT l_found THEN

              l_out := .....

              assoc_array_str( l_key ) := l_out;
         END IF;
         RETURN l_out;
    END;

http://frakkle.com

I'm posting this via trackback because of a strange posting problem:  (layout is strange and missing the email field?  Yes I am using a crud browser from here... that could be it) 

I have to agree with Hernan.

The simplest saving I can see is an extra column to save on the "run time" calculation.  This does not have to be dangerous (ie potentially different to the date column you have already)Just setup a trigger for whenever the existing date column gets updated(/inserted) to update the extra column.

Another alternative is to use a materialised view.  On Postgres this is a manual process involving setting up a view and rules, and ig you want it always up to date, triggers again on the source table to update the materialised view whenever the data changes. 

This latter idea would be the fastest - faster than your original view by quite a margin, in fact.  You may then be able to get rid of some (all?) indexes you have already on the existing table - because they would no longer be needed.

One thing I think would be handy that I have on my list of "when I get time" is to write some reasonably automatic code to do materialised views without the manual coding (ala Oracle).  People may use these things more if they were a bit more simple to do.

Link to Need Help Reducing View Calculations page: http://www.justatheory.com/computers/databases/postgresql/reducing_view_calculations.html

I've just started a new contract for a Federal department where an old grants management system is being replaced with a PostgreSQL/Java based version.  The sister project (sub project really) is a data warehouse.  The choices were Oracle or PostgreSQL (PostgreSQL was what attracted me to the contract actually)

The argument that I have been unable to win in putting together a warehouse on PostgreSQL comes down to tool maturity - ie the risk involved in something "not proven" so it is almost certainly going to be built using Oracle Warehouse Builder and a BI tool tbd.

I have a long history with databases, and experience with PostgreSQL that dates to the beginning of version 7, however I've never been involved in formal datawarehousing or ETL - so I can't speak with the authority I would prefer ;-)

From my research (mostly involving asking Liam at Fujitsu) Bizgres which seems to be still at the "not finished" stage, and Jasper.  I have experience in Jasper products from some time back - they looked very good then - so I can't wait to try out JasperETL.

In any case I am likely to do a parallel run of the work with OWB using Jasper/Postgres to see how they go in my own time.  I would welcome any comments on all this - particularly if they can be backed up with real-world datawarehousing projects.

For those wondering about this blog, family illness has kept me from this for some time, unfortunately... something that is now coming to an end in a good way.

Cheers,

Mathew Frank (http://frakkle.com)

<?php
if (!function_exists('mime_content_type')) {
	function mime_content_type($filename) {
		$idx = strtolower(end( explode( '.', $filename )) );
		$mimet = array(	'ai' =>'application/postscript',
			'aif' =>'audio/x-aiff',
			'aifc' =>'audio/x-aiff',
			'aiff' =>'audio/x-aiff',
			'asc' =>'text/plain',
			'atom' =>'application/atom+xml',
			'avi' =>'video/x-msvideo',
			'bcpio' =>'application/x-bcpio',
			'bmp' =>'image/bmp',
			'cdf' =>'application/x-netcdf',
			'cgm' =>'image/cgm',
			'cpio' =>'application/x-cpio',
			'cpt' =>'application/mac-compactpro',
			'crl' =>'application/x-pkcs7-crl',
			'crt' =>'application/x-x509-ca-cert',
			'csh' =>'application/x-csh',
			'css' =>'text/css',
			'dcr' =>'application/x-director',
			'dir' =>'application/x-director',
			'djv' =>'image/vnd.djvu',
			'djvu' =>'image/vnd.djvu',
			'doc' =>'application/msword',
			'dtd' =>'application/xml-dtd',
			'dvi' =>'application/x-dvi',
			'dxr' =>'application/x-director',
			'eps' =>'application/postscript',
			'etx' =>'text/x-setext',
			'ez' =>'application/andrew-inset',
			'gif' =>'image/gif',
			'gram' =>'application/srgs',
			'grxml' =>'application/srgs+xml',
			'gtar' =>'application/x-gtar',
			'hdf' =>'application/x-hdf',
			'hqx' =>'application/mac-binhex40',
			'html' =>'text/html',
			'html' =>'text/html',
			'ice' =>'x-conference/x-cooltalk',
			'ico' =>'image/x-icon',
			'ics' =>'text/calendar',
			'ief' =>'image/ief',
			'ifb' =>'text/calendar',
			'iges' =>'model/iges',
			'igs' =>'model/iges',
			'jpe' =>'image/jpeg',
			'jpeg' =>'image/jpeg',
			'jpg' =>'image/jpeg',
			'js' =>'application/x-javascript',
			'kar' =>'audio/midi',
			'latex' =>'application/x-latex',
			'm3u' =>'audio/x-mpegurl',
			'man' =>'application/x-troff-man',
			'mathml' =>'application/mathml+xml',
			'me' =>'application/x-troff-me',
			'mesh' =>'model/mesh',
			'mid' =>'audio/midi',
			'midi' =>'audio/midi',
			'mif' =>'application/vnd.mif',
			'mov' =>'video/quicktime',
			'movie' =>'video/x-sgi-movie',
			'mp2' =>'audio/mpeg',
			'mp3' =>'audio/mpeg',
			'mpe' =>'video/mpeg',
			'mpeg' =>'video/mpeg',
			'mpg' =>'video/mpeg',
			'mpga' =>'audio/mpeg',
			'ms' =>'application/x-troff-ms',
			'msh' =>'model/mesh',
			'mxu m4u' =>'video/vnd.mpegurl',
			'nc' =>'application/x-netcdf',
			'oda' =>'application/oda',
			'ogg' =>'application/ogg',
			'pbm' =>'image/x-portable-bitmap',
			'pdb' =>'chemical/x-pdb',
			'pdf' =>'application/pdf',
			'pgm' =>'image/x-portable-graymap',
			'pgn' =>'application/x-chess-pgn',
			'php' =>'application/x-httpd-php',
			'php4' =>'application/x-httpd-php',
			'php3' =>'application/x-httpd-php',
			'phtml' =>'application/x-httpd-php',
			'phps' =>'application/x-httpd-php-source',
			'png' =>'image/png',
			'pnm' =>'image/x-portable-anymap',
			'ppm' =>'image/x-portable-pixmap',
			'ppt' =>'application/vnd.ms-powerpoint',
			'ps' =>'application/postscript',
			'qt' =>'video/quicktime',
			'ra' =>'audio/x-pn-realaudio',
			'ram' =>'audio/x-pn-realaudio',
			'ras' =>'image/x-cmu-raster',
			'rdf' =>'application/rdf+xml',
			'rgb' =>'image/x-rgb',
			'rm' =>'application/vnd.rn-realmedia',
			'roff' =>'application/x-troff',
			'rtf' =>'text/rtf',
			'rtx' =>'text/richtext',
			'sgm' =>'text/sgml',
			'sgml' =>'text/sgml',
			'sh' =>'application/x-sh',
			'shar' =>'application/x-shar',
			'shtml' =>'text/html',
			'silo' =>'model/mesh',
			'sit' =>'application/x-stuffit',
			'skd' =>'application/x-koan',
			'skm' =>'application/x-koan',
			'skp' =>'application/x-koan',
			'skt' =>'application/x-koan',
			'smi' =>'application/smil',
			'smil' =>'application/smil',
			'snd' =>'audio/basic',
			'spl' =>'application/x-futuresplash',
			'src' =>'application/x-wais-source',
			'sv4cpio' =>'application/x-sv4cpio',
			'sv4crc' =>'application/x-sv4crc',
			'svg' =>'image/svg+xml',
			'swf' =>'application/x-shockwave-flash',
			't' =>'application/x-troff',
			'tar' =>'application/x-tar',
			'tcl' =>'application/x-tcl',
			'tex' =>'application/x-tex',
			'texi' =>'application/x-texinfo',
			'texinfo' =>'application/x-texinfo',
			'tgz' =>'application/x-tar',
			'tif' =>'image/tiff',
			'tiff' =>'image/tiff',
			'tr' =>'application/x-troff',
			'tsv' =>'text/tab-separated-values',
			'txt' =>'text/plain',
			'ustar' =>'application/x-ustar',
			'vcd' =>'application/x-cdlink',
			'vrml' =>'model/vrml',
			'vxml' =>'application/voicexml+xml',
			'wav' =>'audio/x-wav',
			'wbmp' =>'image/vnd.wap.wbmp',
			'wbxml' =>'application/vnd.wap.wbxml',
			'wml' =>'text/vnd.wap.wml',
			'wmlc' =>'application/vnd.wap.wmlc',
			'wmlc' =>'application/vnd.wap.wmlc',
			'wmls' =>'text/vnd.wap.wmlscript',
			'wmlsc' =>'application/vnd.wap.wmlscriptc',
			'wmlsc' =>'application/vnd.wap.wmlscriptc',
			'wrl' =>'model/vrml',
			'xbm' =>'image/x-xbitmap',
			'xht' =>'application/xhtml+xml',
			'xhtml' =>'application/xhtml+xml',
			'xls' =>'application/vnd.ms-excel',
			'xml xsl' =>'application/xml',
			'xpm' =>'image/x-xpixmap',
			'xslt' =>'application/xslt+xml',
			'xul' =>'application/vnd.mozilla.xul+xml',
			'xwd' =>'image/x-xwindowdump',
			'xyz' =>'chemical/x-xyz',
			'zip' =>'application/zip'
		);

		if (isset( $mimet[$idx] )) {
			return $mimet[$idx];
		} else {
			return 'application/octet-stream';
		}
	}
}
?>

Human-Anatomy Pictures