Difference between revisions of "Job Module"
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}; | }; | ||
</pre> | </pre> | ||
− | * The following query demonstrates how the results of an asynchronously executed query can be returned in a single query. Please note that this is not the common way how | + | * The following query demonstrates how the results of an asynchronously executed query can be returned in a single query. Please note that this is not the common way how these functions are used in practice (better use [[#Parallel Execution|Parallel Execution]] within a single query): |
<pre class='brush:xquery'> | <pre class='brush:xquery'> | ||
let $query := async:eval('(1 to 10000000)[. = 1]') | let $query := async:eval('(1 to 10000000)[. = 1]') |
Revision as of 16:20, 27 March 2016
This XQuery Module provides functions for evaluating XQuery expressions in separate threads. Query execution can both be parallelized and postponed to be executed asynchronously.
Contents
Conventions
All functions in this module are assigned to the http://basex.org/modules/async
namespace, which is statically bound to the async
prefix. Errors will be bound to the same prefix.
Parallelized Execution
Parallel query execution is recommendable if you have various calls that require a lot of time, but cannot be sped up by rewriting the code. This is e. g. the case if external URLs are called. If you are parallelizing local data reads (such as accessing a database), your single-threaded query will usually be faster, because parallelized access to disk data will often lead to randomized access patterns, which can hardly be optimized by your HD or SSD.
async:fork-join
Signatures | async:fork-join($functions as function(*)*) as item()* async:fork-join($functions as function(*)*, $options as map(xs:string, xs:string)) as item()* |
Summary | This function executes the supplied (non-updating) functions in parallel. The following $options are available:
|
Examples |
async:fork-join( for $i in 1 to 2 return function() { prof:sleep(1000) } )
let $funcs := for $segment in 1 to 4 let $url := 'http://url.com/path' || $segment return function() { http:send-request((), $url) } return async:fork-join($funcs, map { 'threads': 2 }) |
Errors | unexpected : an unexpected error occurred while running a query or function in a separate thread.out-of-range : a supplied option is out of range. |
Asynchronous Execution
Asynchronous query execution is recommendable if a client does not, or cannot, wait until a request is fully processed. This is e. g. the case with web browsers, which will usually cancel a request after a specific timeout. In such cases, you can use asynchronous execution to trigger another server-side process, which will start the time-consuming process, and fetch the result later on as soon as it is available.
async:eval
Signatures | async:eval($query as xs:string) as xs:string async:eval($query as xs:string, $bindings as map(*)) as xs:string async:eval($query as xs:string, $bindings as map(*), $options as map(xs:string, xs:string)) as xs:string |
Summary | Prepares the supplied $query string for asynchronous execution and returns a query id. The query will be queued as described in the article on Transaction Management, and the result will be cached in main-memory until it is fetched via async:result, or until ASYNCTIMEOUT is exceeded.Variables and context items can be declared via $bindings (see xquery:eval for more details). The $options parameter contains evaluation options:
|
Errors | updating : the query contains update operations.
|
Examples |
declare %rest:POST("{$query}") %rest:path('/eval') function local:eval($query) { async:eval($query) }; |
async:update
Signatures | async:update($query as xs:string) as xs:string async:update($query as xs:string, $bindings as map(*)) as xs:string async:update($query as xs:string, $bindings as map(*), $options as map(xs:string, xs:string)) as xs:string |
Summary | Prepares the supplied $query string for asynchronous execution and returns a query id. The query will be queued as described in the article on Transaction Management.See async:eval for information on the $bindings and $options arguments.
|
Errors | non-updating : the query does not contain any update operations. |
Examples |
|
async:result
Signatures | async:result($id as xs:string) as item()*
|
Summary | Returns the result of an asynchronously executed query with the specified query $id :
|
Errors | is-running : the query is still running.unknown : the supplied query id is unknown: The query result may already have been retrieved, or query execution may have been stopped. |
Examples |
declare %rest:path('/result/{$id}') function local:result($id) { async:result($id) };
let $query := async:eval('(1 to 10000000)[. = 1]') return ( hof:until( function($result) { async:finished($query) }, function($curr) { prof:sleep(10) }, () ), async:result($query) ) |
async:finished
Signatures | async:finished($id as xs:string) as xs:boolean
|
Summary | Indicates if the evaluation of a query with the specified query $id has finished. If false is returned, the query is still running. An error will be raised if the query result was not cached or has already been retrieved.
|
Errors | unknown : the supplied query id is unknown: The query result may already have been retrieved, or query execution may have been stopped. |
async:stop
Signatures | async:stop($id as xs:string) as empty-sequence()
|
Summary | Cancels the execution of a query with the specified query $id , or drops the query result if it has already been executed.
|
Errors | unknown : the supplied query id is unknown: The query result may already have been retrieved, or query execution may have been stopped. |
async:ids
Signatures | async:ids() as xs:string*
|
Summary | Returns the ids of all queries that are either being executed asynchronously, or that have been executed and the results of which have been cached. |
Examples |
|
Errors
Code | Description |
---|---|
unexpected
|
An unexpected error occurred while running a query or function in a separate thread. |
out-of-range
|
The supplied option is out of range. |
updating
|
A query is expected to be non-updating, but it performs updates. |
non-updating
|
A query is expected to be updating, but it does not perform updates. |
unknown
|
The supplied query id is unknown or not available anymore. |
is-running
|
A query is still running. |
Changelog
The module was introduced with Version 8.5.