Juri Leino line-o

eXist-db Query Optimizer and Index usage

I put together some findings I gathered over the years on how small adjustements to XPath queries can lead to better performance. These are not definitive and should be tested if they apply to specific slow running queries you have issues with. I assume you have profiled your queries before in the bundled monex application. Here is a bit of documentation on this topic to help you get started: http://exist-db.org/exist/apps/doc/indexing.xml?field=all&id=D3.19#check-usage On a typical local instance this is available at: http://localhost:8080/exist/apps/monex/profiling.html

	(:
	explore if the proposed XQuery 4 function fn:type can be used
	to inspect sequences of items to find the most specific shared
	type among them
	:)
	declare namespace ist="//line-o.de/ns/inspect-sequence-types";

	declare function ist:find-shared-type ($acc as xs:string, $next as xs:string) as xs:string* {
	let $count-a := count($acc)
	let $count-n := count($next)

	xquery version "3.1";

	declare namespace enc="//-o/ns/xquery/encoding";

	import module namespace bin="http://expath.org/ns/binary";

	declare function enc:fix ($string as xs:string) as xs:string {
	analyze-string($string, "(\\u00([0-9a-z]{2})\\u00([0-9a-z]{2}))")/element()
	=> for-each(enc:process#1)
	=> string-join("")

	xquery version "3.1";

	module namespace emt="//external-module-test";

	declare function emt:transform($node as node()) as node()+ {
	typeswitch ($node)
	case document-node() return document { emt:transform($node/element()) }
	case attribute(xml:id) return (
	attribute old-id { $node/string() },
	attribute xml:id { "s" \|\| $node }

	import module namespace array="http://www.w3.org/2005/xpath-functions/array";
	import module namespace map="http://www.w3.org/2005/xpath-functions/map";

	declare namespace _="//line-o.de/ns/underline";

	declare function _:nth-item ($sequence as item(), $pos as xs:integer) as item() {
	$sequence[$pos]
	};

	declare function _:reduce-sequences (

	module namespace prob = "//line-o.de/ns/prob";

	declare namespace map = "http://www.w3.org/2005/xpath-functions/map";
	declare namespace array = "http://www.w3.org/2005/xpath-functions/array";

	(: select by p from prepared sequence of options :)
	declare
	function prob:select-by-p($options as array()+, $p as xs:double) as item() {
	fold-left($options, (),
	prob:select(?, ?, $p)

	<html>
	<body>
	<script type="text/javascript"><![CDATA[ console.log(true && 1 < 2) ]]></script>
	</body>
	</html>

	xquery version "3.1";

	module namespace orcid="orcid/validate";

	declare variable $orcid:R := 2;
	declare variable $orcid:M := 11;
	declare variable $orcid:format := '^(\d{4}-\d{4}-\d{4}-\d{3}\|\d{15})[0-9X]$';
	declare variable $orcid:is-valid-format := matches(?, $orcid:format);
	declare variable $orcid:expected-sum := map{
	'1':1, '2':2, '3':3, '4':4, '5':5, '6':6, '7':7, '8':8, '9':9, 'X':10

	0600 (.rw-------) -> 0700 (.rwx------)
	0755 (.rwxr-xr-x) -> 0755 (.rwxr-xr-x)
	0660 (.rw-rw----) -> 0770 (.rwxrwx---)
	0664 (.rw-rw-r--) -> 0775 (.rwxrwxr-x)
	0666 (.rw-rw-rw-) -> 0777 (.rwxrwxrwx)
	0622 (.rw--w--w-) -> 0733 (.rwx-wx-wx)
	0777 (.rwxrwxrwx) -> 0777 (.rwxrwxrwx)

	xquery version "3.1";

	declare function local:safe-effective-boolean-value-if (
	$result as item()*
	) as xs:boolean {
	try {
	if ($result)
	then true()
	else false()
	} catch err:FORG0006 {

Juri Leino line-o

eXist-db Query Optimizer and Index usage

General rules on predicates