Difference between revisions of "XQuery Module"

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This [[Module Library|XQuery Module]] contains functions for evaluating XQuery strings and modules at runtime.
+
This [[Module Library|XQuery Module]] contains functions for parsing and evaluating XQuery strings at runtime, and to run code in parallel.
  
 
=Conventions=
 
=Conventions=
  
All functions in this module are assigned to the <code><nowiki>http://basex.org/modules/xquery</nowiki></code> namespace, which is statically bound to the {{Code|xquery}} prefix.<br/>
+
All functions and errors in this module are assigned to the <code><nowiki>http://basex.org/modules/xquery</nowiki></code> namespace, which is statically bound to the {{Code|xquery}} prefix.<br/>
All errors are assigned to the <code><nowiki>http://basex.org/errors</nowiki></code> namespace, which is statically bound to the {{Code|bxerr}} prefix.
 
  
=Functions=
+
=Dynamic Evaluation=
  
 
==xquery:eval==
 
==xquery:eval==
Line 13: Line 12:
 
|-
 
|-
 
| width='120' | '''Signatures'''
 
| width='120' | '''Signatures'''
|{{Func|xquery:eval|$query as xs:string|item()*}}<br />{{Func|xquery:eval|$query as xs:string, $bindings as map(*)|item()*}}<br />{{Func|xquery:eval|$query as xs:string, $bindings as map(*), $options as map(xs:string, xs:string)|item()}}<br />
+
|{{Func|xquery:eval|$query as xs:string|item()*}}<br />{{Func|xquery:eval|$query as xs:string, $bindings as map(*)?|item()*}}<br />{{Func|xquery:eval|$query as xs:string, $bindings as map(*)?, $options as map(*)?|item()*}}<br />
 
|-
 
|-
 
| '''Summary'''
 
| '''Summary'''
Line 23: Line 22:
 
* {{Code|permission}}: the query will be evaluated with the specified permissions (see [[User Management]]).
 
* {{Code|permission}}: the query will be evaluated with the specified permissions (see [[User Management]]).
 
* {{Code|timeout}}: query execution will be interrupted after the specified number of seconds.
 
* {{Code|timeout}}: query execution will be interrupted after the specified number of seconds.
* {{Code|memory}}: query execution will be interrupted if the specified number of megabytes will be exceeded. This check works best if only one process is running at the same time.
+
* {{Code|memory}}: query execution will be interrupted if the specified number of megabytes will be exceeded. This check works best if only one process is running at the same time. Moreover, please note that this option enforces garbage collection, so it will take some additional time, and it requires GC to be enabled in your JVM.
 +
* {{Code|base-uri}}: set [https://www.w3.org/TR/xquery-31/#dt-static-base-uri base-uri property] for the query. This URI will be used when resolving relative URIs by functions such as {{Code|fn:doc}}.
 +
* {{Code|pass}}: passes on the original error info (line and column number, optional file uri). By default, this option is {{Code|false}}.
 
|-
 
|-
 
| '''Errors'''
 
| '''Errors'''
|{{Error|BXXQ0001|#Errors}} the query contains [[XQuery Update#Updating Expressions|updating expressions]].<br/>{{Error|BXXQ0003|#Errors}} insufficient permissions for evaluating the query.<br/>{{Error|BXXQ0004|#Errors}} query execution exceeded timeout or memory constraints.<br/>{{Error|FOTY0013|#Errors}} the expression yields function items.<br/>Any other error that may occur while evaluating the query.
+
|{{Error|update|#Errors}} the query contains [[XQuery Update#Updating Expressions|updating expressions]].<br/>{{Error|permission|#Errors}} insufficient permissions for evaluating the query.<br/>{{Error|timeout|#Errors}} query execution exceeded timeout.<br/>{{Error|limit|#Errors}} query execution exceeded memory limit.<br/>{{Error|nested|#Errors}} nested query evaluation is not allowed.<br/>Any other error that may occur while evaluating the query.
 
|-
 
|-
 
| '''Examples'''
 
| '''Examples'''
Line 62: Line 63:
 
|}
 
|}
  
==xquery:update==
+
==xquery:eval-update==
  
 
{| width='100%'
 
{| width='100%'
 
|-
 
|-
 
| width='120' | '''Signatures'''
 
| width='120' | '''Signatures'''
|{{Func|xquery:update|$query as xs:string|item()*}}<br />{{Func|xquery:update|$query as xs:string, $bindings as map(*)|item()*}}<br />{{Func|xquery:update|$query as xs:string, $bindings as map(*), $options as map(xs:string, xs:string)|item()}}<br />
+
|{{Func|xquery:eval-update|$query as xs:string|item()*}}<br />{{Func|xquery:eval-update|$query as xs:string, $bindings as map(*)?|item()*}}<br />{{Func|xquery:eval-update|$query as xs:string, $bindings as map(*)?, $options as map(*)?|item()}}<br />
 
|-
 
|-
 
| '''Summary'''
 
| '''Summary'''
|Evaluates {{Code|$query}} as updating XQuery expression at runtime.<br/>All updates will be added to the [[XQuery Update#Pending Update List|Pending Update List]] of the main query and performed after the evaluation of the main query.<br />The semantics of the {{Code|$bindings}} and {{Code|$options}} parameters is the same as for [[#xquery:eval|xquery:eval]].
+
|Evaluates {{Code|$query}} as updating XQuery expression at runtime.<br/>All updates will be added to the [[XQuery Update#Pending Update List|Pending Update List]] of the main query and performed after the evaluation of the main query.<br />The rules of the {{Code|$bindings}} and {{Code|$options}} parameters are the same as for [[#xquery:eval|xquery:eval]].
 
|-
 
|-
 
| '''Errors'''
 
| '''Errors'''
|{{Error|BXXQ0002|#Errors}} the query contains no [[XQuery Update#Updating Expressions|updating expressions]].<br/>{{Error|BXXQ0003|#Errors}} insufficient permissions for evaluating the query.<br/>{{Error|BXXQ0004|#Errors}} query execution exceeded timeout or memory constraints.<br/>{{Error|FOTY0013|#Errors}} the expression yields function items.<br/>Any other error that may occur while evaluating the query.
+
|{{Error|update|#Errors}} the query contains no [[XQuery Update#Updating Expressions|updating expressions]].<br/>{{Error|permission|#Errors}} insufficient permissions for evaluating the query.<br/>{{Error|timeout|#Errors}} query execution exceeded timeout.<br/>{{Error|limit|#Errors}} query execution exceeded memory limit.<br/>{{Error|nested|#Errors}} nested query evaluation is not allowed.<br/>Any other error that may occur while evaluating the query.
 
|}
 
|}
 +
 +
==xquery:invoke==
 +
 +
{| width='100%'
 +
|-
 +
| width='120' | '''Signatures'''
 +
|{{Func|xquery:invoke|$uri as xs:string|item()*}}<br />{{Func|xquery:invoke|$uri as xs:string, $bindings as map(*)?|item()*}}<br />{{Func|xquery:invoke|$uri as xs:string, $bindings as map(*)?, $options as map(*)?|item()*}}<br />
 +
|-
 +
| '''Summary'''
 +
|Evaluates the XQuery module located at {{Code|$uri}} at runtime and returns the resulting items. A relative URI will be resolved against the static base URI of the query.<br />The rules of the {{Code|$bindings}} and {{Code|$options}} parameters are the same as for [[#xquery:eval|xquery:eval]].
 +
|-
 +
| '''Errors'''
 +
|{{Error|update|#Errors}} the expression contains [[XQuery Update#Updating Expressions|updating expressions]].<br/>{{Error|permission|#Errors}} insufficient permissions for evaluating the query.<br/>{{Error|timeout|#Errors}} query execution exceeded timeout.<br/>{{Error|nested|#Errors}} nested query evaluation is not allowed.<br/>Any other error that may occur while evaluating the query.
 +
|}
 +
 +
==xquery:invoke-update==
 +
 +
{| width='100%'
 +
|-
 +
| width='120' | '''Signatures'''
 +
|{{Func|xquery:invoke-update|$uri as xs:string|item()*}}<br />{{Func|xquery:invoke-update|$uri as xs:string, $bindings as map(*)?|item()*}}<br />{{Func|xquery:invoke-update|$uri as xs:string, $bindings as map(*)?, $options as map(*)?|item()*}}<br />
 +
|-
 +
| '''Summary'''
 +
|Evaluates the updating XQuery module located at {{Code|$uri}} at runtime. A relative URI will be resolved against the static base URI of the query.<br />The rules of the {{Code|$bindings}} and {{Code|$options}} parameters are the same as for [[#xquery:eval|xquery:eval]].
 +
|-
 +
| '''Errors'''
 +
|{{Error|update|#Errors}} the expression contains no [[XQuery Update#Updating Expressions|updating expressions]].<br/>{{Error|permission|#Errors}} insufficient permissions for evaluating the query.<br/>{{Error|timeout|#Errors}} query execution exceeded timeout.<br/>{{Error|nested|#Errors}} nested query evaluation is not allowed.<br/>Any other error that may occur while evaluating the query.
 +
|}
 +
 +
=XQuery Parsing=
  
 
==xquery:parse==
 
==xquery:parse==
Line 81: Line 112:
 
|-
 
|-
 
| width='120' | '''Signatures'''
 
| width='120' | '''Signatures'''
|{{Func|xquery:parse|$query as xs:string|item()*}}<br />{{Func|xquery:parse|$query as xs:string, $options as map(*)|item()}}<br />
+
|{{Func|xquery:parse|$query as xs:string|item()?}}<br />{{Func|xquery:parse|$query as xs:string, $options as map(*)?|item()?}}<br />
 
|-
 
|-
 
| '''Summary'''
 
| '''Summary'''
Line 87: Line 118:
 
* {{Code|compile}}: additionally compiles the query after parsing it. By default, this option is {{Code|false}}.
 
* {{Code|compile}}: additionally compiles the query after parsing it. By default, this option is {{Code|false}}.
 
* {{Code|plan}}: returns an XML representation of the internal query plan. By default, this option is {{Code|true}}. The naming of the expressions in the query plan may change over time
 
* {{Code|plan}}: returns an XML representation of the internal query plan. By default, this option is {{Code|true}}. The naming of the expressions in the query plan may change over time
 +
* {{Code|pass}}: passes on the original error info (line and column number, optional file uri). By default, this option is {{Code|false}}.
 +
* {{Code|base-uri}}: set [https://www.w3.org/TR/xquery-31/#dt-static-base-uri base-uri property] for the query. This URI will be used when resolving relative URIs by functions such as {{Code|fn:doc}}.
 
|-
 
|-
 
| '''Errors'''
 
| '''Errors'''
Line 107: Line 140:
  
 
==xquery:parse-uri==
 
==xquery:parse-uri==
 
{{Mark|Introduced with Version 8.4}}:
 
  
 
{| width='100%'
 
{| width='100%'
 
|-
 
|-
 
| width='120' | '''Signatures'''
 
| width='120' | '''Signatures'''
|{{Func|xquery:parse-uri|$uri as xs:string|item()*}}<br />{{Func|xquery:parse-uri|$uri as xs:string, $options as map(*)|item()*}}<br />
+
|{{Func|xquery:parse-uri|$uri as xs:string|item()?}}<br />{{Func|xquery:parse-uri|$uri as xs:string, $options as map(*)?|item()?}}<br />
 
|-
 
|-
 
| '''Summary'''
 
| '''Summary'''
|Parses the XQuery module located at {{Code|$uri}} and returns the resulting query plan. The {{Code|$options}} parameter is the same as for [[#xquery:parse|xquery:parse]].
+
|Parses the XQuery module located at {{Code|$uri}} and returns the resulting query plan. A relative URI will be resolved against the static base URI of the query. The rules for the {{Code|$options}} parameter are the same as for [[#xquery:parse|xquery:parse]].
 
|-
 
|-
 
| '''Errors'''
 
| '''Errors'''
Line 122: Line 153:
 
|}
 
|}
  
==xquery:invoke==
+
=Parallelized Execution=
 +
 
 +
Parallel query execution is recommendable if you have various calls that require a lot of time, but that cannot be sped up by rewriting the code. This is e. g. the case if external URLs are called. If you are parallelizing local data reads (such as the access to a database), single-threaded queries will usually be faster, because parallelized access to disk data often results in randomized access patterns, which will rarely be optimized by the caching strategies of HDDs, SSDs, or the operating system.
  
{{Mark|Updated with Version 8.4}}: will be renamed to {{Code|xquery:eval-uri}}
+
==xquery:fork-join==
  
 
{| width='100%'
 
{| width='100%'
 
|-
 
|-
 
| width='120' | '''Signatures'''
 
| width='120' | '''Signatures'''
|{{Func|xquery:invoke|$uri as xs:string|item()*}}<br />{{Func|xquery:invoke|$uri as xs:string, $bindings as map(*)|item()*}}<br />{{Func|xquery:invoke|$uri as xs:string, $bindings as map(*), $options as map(*)|item()*}}<br />
+
|{{Func|xquery:fork-join|$functions as function(*)*|item()*}}
 
|-
 
|-
| '''Summary'''
+
|'''Summary'''
|Evaluates the XQuery module located at {{Code|$uri}} at runtime and returns the resulting items.  Database nodes in the result will be copied and returned instead.<br />The semantics of the {{Code|$bindings}} and {{Code|$options}} parameters is the same as for [[#xquery:eval|xquery:eval]].
+
|This function executes the supplied (non-updating) functions in parallel.
 
|-
 
|-
| '''Errors'''
+
| '''Examples'''
|{{Error|BXXQ0001|#Errors}} the expression contains [[XQuery Update#Updating Expressions|updating expressions]].<br/>{{Error|BXXQ0003|#Errors}} insufficient permissions for evaluating the query.<br/>{{Error|BXXQ0004|#Errors}} query execution exceeded timeout.<br/>{{Error|FOTY0013|#Errors}} the expression yields function items.<br/>Any other error that may occur while evaluating the query.
+
|
|}
+
* The following function sleeps in parallel; it will be finished in 1 second if your system has at least 2 cores:
 
+
<pre class='brush:xquery'>
==xquery:type==
+
let $f := function() { prof:sleep(1000) }
 
+
return xquery:fork-join(($f, $f))
{| width='100%'
+
</pre>
 +
* In the following query, up to four URLs will be requested in parallel:
 +
<pre class='brush:xquery'>
 +
xquery:fork-join(
 +
  for $segment in 1 to 4
 +
  let $url := 'http://url.com/path/' || $segment
 +
  return function() { http:send-request((), $url) }
 +
)
 +
</pre>
 
|-
 
|-
| width='120' | '''Signatures'''
+
|'''Errors'''
|{{Func|xquery:type|$expr as item()*|item()*}}
+
|{{Error|error|#Errors}} an unexpected error occurred.
|-
 
| '''Summary'''
 
|Similar to {{Code|fn:trace($expr, $msg)}}, but instead of a user-defined message, it emits the compile-time type and estimated result size of its argument.
 
 
|}
 
|}
  
Line 155: Line 193:
 
|Description
 
|Description
 
|-
 
|-
|{{Code|BXXQ0001}}
+
|{{Code|permission}}
|The specified query contains [[XQuery Update#Updating Expressions|updating expressions]].
+
|Insufficient permissions for evaluating the query.
 +
|-
 +
|{{Code|update}}
 +
|[[XQuery Update#Updating Expressions|updating expression]] found or expected.
 +
|-
 +
|{{Code|timeout}}
 +
|Query execution exceeded timeout.
 
|-
 
|-
|{{Code|BXXQ0002}}
+
|{{Code|memory}}
|The specified query contains no [[XQuery Update#Updating Expressions|updating expressions]].
+
|Query execution exceeded memory limit.
 
|-
 
|-
|{{Code|BXXQ0003}}
+
|{{Code|nested}}
|Insufficient permissions for evaluating the query.
+
|Nested query evaluation is not allowed.
 
|-
 
|-
|{{Code|BXXQ0004}}
+
|{{Code|error}}
|Query execution exceeded timeout.
+
|An unexpected error occurred.
 
|}
 
|}
  
 
=Changelog=
 
=Changelog=
 +
 +
;Version 9.0
 +
 +
* Added: [[#xquery:invoke-update|xquery:invoke-update]]
 +
* Updated: [[#xquery:eval|xquery:eval]]: {{Code|pass}} option added
 +
* Updated: [[#xquery:parse|xquery:parse]], [[#xquery:parse-uri|xquery:parse-uri]]: {{Code|base-uri}} option added
 +
* Updated: xquery:update renamed to [[#xquery:eval-update|xquery:eval-update]]
 +
* Updated: error codes updated; errors now use the module namespace
 +
 +
;Version 8.5
 +
 +
* Added: [[#xquery:fork-join|xquery:fork-join]]
 +
* Updated: [[#xquery:eval|xquery:eval]]: {{Code|base-uri}} option added
 +
* Updated: Relative URIs will always be resolved against the static base URI of the query
 +
* Deleted: xquery:type (moved to [[Profiling Module]]
  
 
;Version 8.4
 
;Version 8.4
 +
 
* Added: [[#xquery:parse-uri|xquery:parse-uri]]
 
* Added: [[#xquery:parse-uri|xquery:parse-uri]]
 +
* Updated: [[#xquery:parse|xquery:parse]]: {{Code|pass}} option added
  
 
;Version 8.0
 
;Version 8.0
* Added: [[#xquery:update|xquery:update]], [[#xquery:parse|xquery:parse]]
+
 
 +
* Added: xquery:update, [[#xquery:parse|xquery:parse]]
 
* Deleted: [[#xquery:evaluate|xquery:evaluate]] (opened databases will now be closed by main query)
 
* Deleted: [[#xquery:evaluate|xquery:evaluate]] (opened databases will now be closed by main query)
  
 
;Version 7.8.2
 
;Version 7.8.2
 +
 
* Added: {{Code|$options}} argument
 
* Added: {{Code|$options}} argument
  
 
;Version 7.8
 
;Version 7.8
 +
 
* Added: [[#xquery:evaluate|xquery:evaluate]]
 
* Added: [[#xquery:evaluate|xquery:evaluate]]
 
* Updated: used variables must be explicitly declared in the query string.
 
* Updated: used variables must be explicitly declared in the query string.
  
 
This module was introduced with Version 7.3. Functions have been adopted from the obsolete Utility Module.
 
This module was introduced with Version 7.3. Functions have been adopted from the obsolete Utility Module.
 
[[Category:XQuery]]
 

Revision as of 08:59, 18 August 2018

This XQuery Module contains functions for parsing and evaluating XQuery strings at runtime, and to run code in parallel.

Conventions

All functions and errors in this module are assigned to the http://basex.org/modules/xquery namespace, which is statically bound to the xquery prefix.

Dynamic Evaluation

xquery:eval

Signatures xquery:eval($query as xs:string) as item()*
xquery:eval($query as xs:string, $bindings as map(*)?) as item()*
xquery:eval($query as xs:string, $bindings as map(*)?, $options as map(*)?) as item()*
Summary Evaluates the supplied $query string as XQuery expression and returns the resulting items.
The evaluated query has its own query context. If a returned node is stored in a database, a main-memory copy will be returned as result, because the referenced database is closed after query execution and will not be accessible anymore.
Variables and context items can be declared via $bindings. The specified keys must be QNames or strings:
  • If a key is a QName, it will be directly adopted as variable name.
  • It a key is a string, it may be prefixed with a dollar sign. Namespace can be specified using the Clark Notation.
  • If the specified string is empty, the value will be bound to the context item.

The $options parameter contains evaluation options:

  • permission: the query will be evaluated with the specified permissions (see User Management).
  • timeout: query execution will be interrupted after the specified number of seconds.
  • memory: query execution will be interrupted if the specified number of megabytes will be exceeded. This check works best if only one process is running at the same time. Moreover, please note that this option enforces garbage collection, so it will take some additional time, and it requires GC to be enabled in your JVM.
  • base-uri: set base-uri property for the query. This URI will be used when resolving relative URIs by functions such as fn:doc.
  • pass: passes on the original error info (line and column number, optional file uri). By default, this option is false.
Errors update: the query contains updating expressions.
permission: insufficient permissions for evaluating the query.
timeout: query execution exceeded timeout.
limit: query execution exceeded memory limit.
nested: nested query evaluation is not allowed.
Any other error that may occur while evaluating the query.
Examples
  • xquery:eval("1+3") returns 4.
  • You can bind the context and e.g. operate on a certain database only:
xquery:eval("//country", map { '': db:open('factbook') })
  • The following expressions use strings as keys. All of them return 'XML':
xquery:eval(".", map { '': 'XML' }),

xquery:eval("declare variable $xml external; $xml", map { 'xml': 'XML' }),

xquery:eval(
  "declare namespace pref='URI';
   declare variable $pref:xml external;
   $pref:xml",
  map { '{URI}xml': 'XML' }
)
  • The following expressions use QNames as keys. All of them return 'XML':
declare namespace pref = 'URI';

xquery:eval("declare variable $xml external; $xml", map { xs:QName('xml'): 'XML' }),

let $query := "declare namespace pref='URI';
               declare variable $pref:xml external;
               $pref:xml"
let $vars := map { xs:QName('pref:xml'): 'XML' }
return xquery:eval($query, $vars)

xquery:eval-update

Signatures xquery:eval-update($query as xs:string) as item()*
xquery:eval-update($query as xs:string, $bindings as map(*)?) as item()*
xquery:eval-update($query as xs:string, $bindings as map(*)?, $options as map(*)?) as item()
Summary Evaluates $query as updating XQuery expression at runtime.
All updates will be added to the Pending Update List of the main query and performed after the evaluation of the main query.
The rules of the $bindings and $options parameters are the same as for xquery:eval.
Errors update: the query contains no updating expressions.
permission: insufficient permissions for evaluating the query.
timeout: query execution exceeded timeout.
limit: query execution exceeded memory limit.
nested: nested query evaluation is not allowed.
Any other error that may occur while evaluating the query.

xquery:invoke

Signatures xquery:invoke($uri as xs:string) as item()*
xquery:invoke($uri as xs:string, $bindings as map(*)?) as item()*
xquery:invoke($uri as xs:string, $bindings as map(*)?, $options as map(*)?) as item()*
Summary Evaluates the XQuery module located at $uri at runtime and returns the resulting items. A relative URI will be resolved against the static base URI of the query.
The rules of the $bindings and $options parameters are the same as for xquery:eval.
Errors update: the expression contains updating expressions.
permission: insufficient permissions for evaluating the query.
timeout: query execution exceeded timeout.
nested: nested query evaluation is not allowed.
Any other error that may occur while evaluating the query.

xquery:invoke-update

Signatures xquery:invoke-update($uri as xs:string) as item()*
xquery:invoke-update($uri as xs:string, $bindings as map(*)?) as item()*
xquery:invoke-update($uri as xs:string, $bindings as map(*)?, $options as map(*)?) as item()*
Summary Evaluates the updating XQuery module located at $uri at runtime. A relative URI will be resolved against the static base URI of the query.
The rules of the $bindings and $options parameters are the same as for xquery:eval.
Errors update: the expression contains no updating expressions.
permission: insufficient permissions for evaluating the query.
timeout: query execution exceeded timeout.
nested: nested query evaluation is not allowed.
Any other error that may occur while evaluating the query.

XQuery Parsing

xquery:parse

Signatures xquery:parse($query as xs:string) as item()?
xquery:parse($query as xs:string, $options as map(*)?) as item()?
Summary Parses the specified $query string as XQuery module and returns the resulting query plan. The $options parameter influences the output:
  • compile: additionally compiles the query after parsing it. By default, this option is false.
  • plan: returns an XML representation of the internal query plan. By default, this option is true. The naming of the expressions in the query plan may change over time
  • pass: passes on the original error info (line and column number, optional file uri). By default, this option is false.
  • base-uri: set base-uri property for the query. This URI will be used when resolving relative URIs by functions such as fn:doc.
Errors Any error that may occur while parsing the query.
Examples
  • xquery:parse("1 + 3") returns:
<MainModule updating="false">
  <QueryPlan compiled="false">
    <Arith op="+">
      <Int value="1" type="xs:integer"/>
      <Int value="3" type="xs:integer"/>
    </Arith>
  </QueryPlan>
</MainModule>

xquery:parse-uri

Signatures xquery:parse-uri($uri as xs:string) as item()?
xquery:parse-uri($uri as xs:string, $options as map(*)?) as item()?
Summary Parses the XQuery module located at $uri and returns the resulting query plan. A relative URI will be resolved against the static base URI of the query. The rules for the $options parameter are the same as for xquery:parse.
Errors Any error that may occur while parsing the query.

Parallelized Execution

Parallel query execution is recommendable if you have various calls that require a lot of time, but that cannot be sped up by rewriting the code. This is e. g. the case if external URLs are called. If you are parallelizing local data reads (such as the access to a database), single-threaded queries will usually be faster, because parallelized access to disk data often results in randomized access patterns, which will rarely be optimized by the caching strategies of HDDs, SSDs, or the operating system.

xquery:fork-join

Signatures xquery:fork-join($functions as function(*)*) as item()*
Summary This function executes the supplied (non-updating) functions in parallel.
Examples
  • The following function sleeps in parallel; it will be finished in 1 second if your system has at least 2 cores:
let $f := function() { prof:sleep(1000) }
return xquery:fork-join(($f, $f))
  • In the following query, up to four URLs will be requested in parallel:
xquery:fork-join(
  for $segment in 1 to 4
  let $url := 'http://url.com/path/' || $segment
  return function() { http:send-request((), $url) }
)
Errors error: an unexpected error occurred.

Errors

Code Description
permission Insufficient permissions for evaluating the query.
update updating expression found or expected.
timeout Query execution exceeded timeout.
memory Query execution exceeded memory limit.
nested Nested query evaluation is not allowed.
error An unexpected error occurred.

Changelog

Version 9.0
Version 8.5
Version 8.4
Version 8.0
Version 7.8.2
  • Added: $options argument
Version 7.8
  • Added: xquery:evaluate
  • Updated: used variables must be explicitly declared in the query string.

This module was introduced with Version 7.3. Functions have been adopted from the obsolete Utility Module.