[MarkLogic Dev General] About hash map function

[McBeath, Darin W (ELS-STL)]

Not sure, but you might want to perform the update as a separate transaction ... Using xdmp:eval-in.

-----Original Message-----
From: general-bounces at developer.marklogic.com <general-bounces at developer.marklogic.com>
To: 'General Mark Logic Developer Discussion' <general at developer.marklogic.com>
Sent: Mon May 14 17:28:01 2007
Subject: RE: [MarkLogic Dev General] About hash map function

Would this be the appropriate time to ask what the *best* implementation for
a sequence (numeric id generator) is in Mark Logic Xquery? Should have the
usual characteristics: monotonically increasing, thread safe.

The best we've come up with is to store a value in a global document
somewhere and update it; not sure if this any reason to try and improve on
that - any opinions?

-Mike

> -----Original Message-----
> From: general-bounces at developer.marklogic.com 
> [mailto:general-bounces at developer.marklogic.com] On Behalf Of 
> Ian Small
> Sent: Monday, May 14, 2007 5:21 PM
> To: General Mark Logic Developer Discussion
> Subject: RE: [MarkLogic Dev General] About hash map function
> 
> Alternatively, xdmp:query-meters() will return the actual 
> wallclock time as part of its output.  Two potential issues with this:
> - resolution of timer of your operating system may still be "too fast"
> - arguably, using a sledgehammer for a fly, considering the 
> size of the structure that query-meters() returns, when all 
> you want is the wallclock time
> 
> I prefer pure random()-based or hybrid (ie. stable clock + 
> random etc.) approaches myself. 
> 
> ian
> 
> -----Original Message-----
> From: general-bounces at developer.marklogic.com
> [mailto:general-bounces at developer.marklogic.com] On Behalf Of 
> Gerety, Colin
> Sent: Monday, May 14, 2007 2:17 PM
> To: General Mark Logic Developer Discussion
> Subject: RE: [MarkLogic Dev General] About hash map function
> 
> Thanks for pointing out that current-dateTime() is "stable".  
> I had missed that.
> 
> Colin Gerety
> Flatirons Solutions Corporation
> 
> -----Original Message-----
> From: general-bounces at developer.marklogic.com
> [mailto:general-bounces at developer.marklogic.com] On Behalf Of 
> Ryan Grimm
> Sent: Monday, May 14, 2007 3:05 PM
> To: General Mark Logic Developer Discussion
> Subject: Re: [MarkLogic Dev General] About hash map function
> 
> Hi Rashid,
> 
> In XQuery, the current-dateTime() will always return the same 
> value during the execution of the query.  To see this try 
> executing this
> query:
> 
> current-dateTime(),
> xdmp:sleep(5000),
> current-dateTime()
> 
> You'll see that result of current-dateTime() is the same for 
> both calls even though there was a sleep in there for 5 seconds.
> 
> If you're looking for a unique value for some id's you could 
> probably use xdmp:random() to generate an unsigned 64bit 
> integer.  While there is
> 
> a small possibility of xdmp:random() returning the same value 
> twice, the
> 
>   same potential problem exists for xdmp:hash64().
> 
> Hope that helps.
> 
> --Ryan
> 
> 
> Nizamuddin, Rashid wrote:
> > Could anybody please tell me why I am not getting a unique 
> value when
> I 
> > execute this loop
> > 
> > *let $cnt := 1 to 5*
> > 
> > *for $c in $cnt*
> > 
> > *return *
> > 
> > *    let $str := xdmp:hash64(string(current-dateTime()))*
> > 
> > *    return $str*
> > 
> > * *
> > 
> > *for each iteration I get the same value. I need to get a 
> unique value
> 
> > to insert in some ids elements.*
> > 
> > * *
> > 
> > *Any help will be appreciated*
> > 
> > * *
> > 
> > *Rashid*
> > 
> > * *
> > 
> > 
> >
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