EXPLAIN¶
Explain or analyze the plan for a given statement.
Table of contents
Description¶
The EXPLAIN command displays the execution plan that the planner generates
for the supplied statement. The plan is returned as a nested object containing
the plan tree.
When issuing EXPLAIN ANALYZE the plan of the statement is executed and
timings of the different phases of the plan are returned.
Note
The content of the returned plan tree as well as the level of detail of the timings of the different phases should be considered experimental and are subject to change in future versions. Also not all plan nodes provide in-depth details.
The output of EXPLAIN ANALYZE also includes a break down of the query
execution if the statement being explained involves queries which are executed
using Lucene.
The output includes verbose low level information per queried shard. Since SQL query expressions do not always have a direct 1:1 mapping to Lucene queries the output may be more complex but in most cases it should still be possible to identify the most expensive parts of a query expression. Some familiarity with Lucene helps in interpreting the output.
A short excerpt of a query breakdown looks like this:
{
"QueryName": "PointRangeQuery",
"QueryDescription": "x:[1 TO 1]",
"Time": 0.004096,
"BreakDown": {
"score": 0,
"match_count": 0,
"build_scorer_count": 0,
"create_weight": 0.004095,
"next_doc": 0,
"match": 0,
"score_count": 0,
"next_doc_count": 0,
"create_weight_count": 1,
"build_scorer": 0,
"advance_count": 0,
"advance": 0
}
}
The time values are in milliseconds. Fields suffixed with _count indicate
how often an operation was invoked.
| field | description |
|---|---|
create_weight |
A Weight object is created
for a query and acts as a
temporary object containing
state. This metric shows how long
this process took. |
build_scorer |
A Scorer object is used to
iterate over documents matching
the query and generate scores for
them. Note that this includes
only the time to create the
scorer, not that actual time
spent on the iteration. |
score |
Shows the time it takes to score
a particular document via its
Scorer. |
next_doc |
Shows the time it takes to determine which document is the next match. |
advance |
A lower level version of
next_doc. |
match |
Some queries use a two-phase
execution, doing an
approximation first, and then
a second more expensive phase.
This metric measures the second
phase. |
Note
Individual timings of the different phases and queries that are profiled do
not sum up to the Total. This is because there is usually additional
initialization that is not measured. Also, certain phases do overlap during
their execution.
Parameters¶
| statement: | The statement for which a plan or plan analysis should be returned. Currently only |
|---|