Hi,
I have a query that's not performing well, even though I have created a
skiplist index. It's a simple query:
127.0.0.1:8529@some4> db._explain("FOR c IN items sort c.created desc limit
10 RETURN c");
Query string:
FOR c IN items sort c.created desc limit 10 RETURN c
Execution plan:
Id NodeType Est. Comment
1 SingletonNode 1 * ROOT
2 EnumerateCollectionNode 1040 - FOR c IN items /* full
collection scan */
3 CalculationNode 1040 - LET #1 = c.`created` /*
attribute expression */ /* collections used: c : items */
4 SortNode 1040 - SORT #1 DESC
5 LimitNode 10 - LIMIT 0, 10
6 ReturnNode 10 - RETURN c
Indexes used:
none
Optimization rules applied:
none
There is no skiplist index used. If I change it like this, thn the index is
used:
127.0.0.1:8529@some4> db._explain("FOR c IN items filter c.created >
1000000 sort c.created desc limit 10 RETURN c");
Query string:
FOR c IN items filter c.created > 1000000 sort c.created desc limit 10
RETURN c
Execution plan:
Id NodeType Est. Comment
1 SingletonNode 1 * ROOT
9 IndexNode 520 - FOR c IN items /* skiplist index scan
*/
5 CalculationNode 520 - LET #3 = c.`created` /* attribute
expression */ /* collections used: c : items */
6 SortNode 520 - SORT #3 DESC
7 LimitNode 10 - LIMIT 0, 10
8 ReturnNode 10 - RETURN c
Indexes used:
By Type Collection Unique Sparse Selectivity
Fields Ranges
9 skiplist items false true n/a [ `created`
] (c.`created` > 1000000)
Optimization rules applied:
Id RuleName
1 move-calculations-up
2 move-filters-up
3 move-calculations-up-2
4 move-filters-up-2
5 use-indexes
6 remove-filter-covered-by-index
7 remove-unnecessary-calculations-2
Now, this is a workaround I could do, but it's not easy to determine a good
value for items.created - a proper value could be a second, a hour or a
day. It's not easy to determine without trying different values.
"items.created" is a numerical timestamp.
Without this workaround the query is very slow.
I don't think it would be difficult to optimize this type of query in
Arangodb? I'm using Arangodb 3.1.3.
Thanks.
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