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added paragraph about explainer

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Jan Steemann 2015-05-13 21:33:16 +02:00
parent 91bf984de7
commit dafa3ef85c
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Documentation/Books/Users/Aql/Invoke.mdpp
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@ -181,15 +181,17 @@ The meaning of the statistics attributes is as follows:
!SECTION Explaining queries !SECTION Explaining queries
If it is unclear how a given query will perform, clients can retrieve a query's execution from If it is unclear how a given query will perform, clients can retrieve a query's execution plan
the AQL query optimizer. This can be achieved by calling the [HTTP REST API](../HttpAqlQuery/README.md) from the AQL query optimizer without actually executing the query. Getting the query execution
for this. Getting the execution plan from the optimizer is called `explain`. plan from the optimizer is called *explaining*.
A query can also be explained from the ArangoShell using `ArangoStatement`s `explain` method. An explain will throw an error if the given query is syntactically invalid. Otherwise, it will
`explain` will throw an error if the given query is syntactically invalid. Otherwise, it will
return the execution plan and some information about what optimizations could be applied to return the execution plan and some information about what optimizations could be applied to
the query. The query will not be executed. the query. The query will not be executed.
Explaining a query can be achieved by calling the [HTTP REST API](../HttpAqlQuery/README.md).
A query can also be explained from the ArangoShell using `ArangoStatement`s `explain` method.
By default, the query optimizer will return what it considers to be the *optimal plan*. The By default, the query optimizer will return what it considers to be the *optimal plan*. The
optimal plan will be returned in the `plan` attribute of the result. If `explain` is optimal plan will be returned in the `plan` attribute of the result. If `explain` is
called with option `allPlans` set to `true`, all plans will be returned in the `plans` called with option `allPlans` set to `true`, all plans will be returned in the `plans`
@ -350,6 +352,19 @@ The following example disables all optimizer rules but `remove-redundant-calcula
arangosh> stmt.explain({ optimizer: { rules: [ "-all", "+remove-redundant-calculations" ] } }); arangosh> stmt.explain({ optimizer: { rules: [ "-all", "+remove-redundant-calculations" ] } });
``` ```
The contents of an execution plan are meant to be machine-readable. To get a human-readable
version of a query's execution plan, the following commnands can be used:
```js
arangosh> var query = "FOR doc IN collection FILTER doc.value > 42 RETURN doc";
arangosh> require("org/arangodb/aql/explainer").explain(query);
```
The above command prints the query's execution plan in the ArangoShell directly, focusing
on the most important information.
!SECTION Parsing queries !SECTION Parsing queries
Clients can use ArangoDB to check if a given AQL query is syntactically valid. ArangoDB provides Clients can use ArangoDB to check if a given AQL query is syntactically valid. ArangoDB provides