[MarkLogic Dev General] Performance of fn:exists(fn:doc($uri))

Geert Josten geert.josten at dayon.nl
Wed Aug 29 11:23:42 PDT 2012

Hi Danny,

Performance should be easy to measure. Call the function from within
QConsole x number of time and request profile output. Do the same while
using xdmp:exists instead of fn:exists. That function works only on
(partially) searchable expression, because it doesn’t retrieve the actual
content. It won’t create a read-lock either, but I’m not sure why you want
one. It won’t prevent duplicate id’s from being generated in concurrent

Kind regards,


*Van:* general-bounces at developer.marklogic.com [mailto:
general-bounces at developer.marklogic.com] *Namens *Danny Sinang
*Verzonden:* woensdag 29 augustus 2012 19:11
*Aan:* general
*Onderwerp:* [MarkLogic Dev General] Performance of fn:exists(fn:doc($uri))


ML support suggested we do this to generate a unique ID for our documents :

declare function choose-uri() as xs:string
       let $uri := fn:concat("/document-", xdmp:random(), ".xml")
       return if (fn:exists(fn:doc($uri))) then choose-uri() else $uri

My question is, will the call to fn:exists(fn:doc($uri)) be fast,
considering that we now have 8 million documents ?

The fn:exists(fn:doc($uri)) call is needed to obtain a read lock, which
will be upgraded to a write lock when xdmp:document-insert is called.


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