[ http://issues.apache.org/jira/browse/DERBY-47?page=all ]
James Synge updated DERBY-47:
-----------------------------
Attachment: Derby47PerformanceTest.java
> Some possible improvements to IN optimization
> ---------------------------------------------
>
> Key: DERBY-47
> URL: http://issues.apache.org/jira/browse/DERBY-47
> Project: Derby
> Issue Type: Improvement
> Components: SQL
> Affects Versions: 10.0.2.0
> Environment: all
> Reporter: Sunitha Kambhampati
> Attachments: derby-47-performance-data.txt,
> Derby47PerformanceTest.java, QueryPlanUniqueIndexAndWordIndexOneTerm.txt,
> QueryPlanUniqueIndexAndWordIndexTwoTerms.txt,
> QueryPlanUniqueIndexOnlyOneTerm.txt, QueryPlanUniqueIndexOnlyTwoTerms.txt
>
>
> Consider a simple case of -
> A table tbl has 10000 rows, there is a primary key index on i1
> and the query in question is
> select * from tbl where i1 in (-1,100000)
> derby does a table scan of the entire table even though the "IN" list has
> only two values and the comparison is on a field that has an index.
> Briefly looking at the code, it seems like we insert a between and use the IN
> list to get the start and stop values for the scan. Thus the range of the
> values in the "IN" list here plays an important role.
> Thus if the query was changed to select * from tbl where i1 in (-1, 1), an
> index scan would be chosen.
> It would be nice if we could do something clever in this case where there is
> clearly an index on the field and the number of values in the IN list is
> known. Maybe use the rowcount estimate and the IN list size to do some
> optimizations.
> - consider the length of the "IN" list to do searches on the table. ie use
> the IN list values to do index key searches on the table,
> -or try to convert it to a join. Use the "IN" list values to create a
> temporary table and do a join. It is most likely that the optimizer will
> choose the table with "IN" list here as the outer table in the join and thus
> will do key searches on the larger table.
> -------------------------------------------------------------------
> some query plans that I logged using derby.language.logQueryPlan=true for
> some similar queries:
> Table has ascending values from 0 - 9999 for i1. primary key index on i1.
> GMT Thread[UT0,5,main] (XID = 19941), (SESSIONID = 0), select * from
> scanfixed where i1 in (-1,9999,9998,9997,9996,9995,9994,9993,9992,9991,9990)
> ******* Project-Restrict ResultSet (2):
> Number of opens = 1
> Rows seen = 10000
> Rows filtered = 9990
> restriction = true
> projection = false
> constructor time (milliseconds) = 0
> open time (milliseconds) = 0
> next time (milliseconds) = 0
> close time (milliseconds) = 0
> restriction time (milliseconds) = 0
> projection time (milliseconds) = 0
> optimizer estimated row count: 750.38
> optimizer estimated cost: 8579.46
> Source result set:
> Table Scan ResultSet for SCANFIXED at read committed isolation level
> using instantaneous share row locking chosen by the optimizer
> Number of opens = 1
> Rows seen = 10000
> Rows filtered = 0
> Fetch Size = 16
> constructor time (milliseconds) = 0
> open time (milliseconds) = 0
> next time (milliseconds) = 0
> close time (milliseconds) = 0
> next time in milliseconds/row = 0
> scan information:
> Bit set of columns fetched=All
> Number of columns fetched=9
> Number of pages visited=417
> Number of rows qualified=10000
> Number of rows visited=10000
> Scan type=heap
> start position:
> null stop position:
> null qualifiers:
> Column[0][0] Id: 0
> Operator: <=
> Ordered nulls: false
> Unknown return value: false
> Negate comparison result: false
> Column[0][1] Id: 0
> Operator: <
> Ordered nulls: false
> Unknown return value: true
> Negate comparison result: true
> optimizer estimated row count: 750.38
> optimizer estimated cost: 8579.46
> ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------
> l
> 2004-10-14 18:59:47.577 GMT Thread[UT0,5,main] (XID = 19216), (SESSIONID =
> 0), select * from scanfixed where i1 in
> (9999,9998,9997,9996,9995,9994,9993,9992,9991,9990) ******* Project-Restrict
> ResultSet (3):
> Number of opens = 1
> Rows seen = 10
> Rows filtered = 0
> restriction = true
> projection = true
> constructor time (milliseconds) = 0
> open time (milliseconds) = 0
> next time (milliseconds) = 0
> close time (milliseconds) = 0
> restriction time (milliseconds) = 0
> projection time (milliseconds) = 0
> optimizer estimated row count: 4.80
> optimizer estimated cost: 39.53
> Source result set:
> Index Row to Base Row ResultSet for SCANFIXED:
> Number of opens = 1
> Rows seen = 10
> Columns accessed from heap = {0, 1, 2, 3, 4, 5, 6, 7, 8}
> constructor time (milliseconds) = 0
> open time (milliseconds) = 0
> next time (milliseconds) = 0
> close time (milliseconds) = 0
> optimizer estimated row count: 4.80
> optimizer estimated cost: 39.53
> Index Scan ResultSet for SCANFIXED using index SCANFIXEDX at
> read committed isolation level using instantaneous share row locking chosen
> by the optimizer
> Number of opens = 1
> Rows seen = 10
> Rows filtered = 0
> Fetch Size = 16
> constructor time (milliseconds) = 0
> open time (milliseconds) = 0
> next time (milliseconds) = 0
> close time (milliseconds) = 0
> next time in milliseconds/row = 0
> scan information:
> Bit set of columns fetched=All
> Number of columns fetched=2
> Number of deleted rows visited=0
> Number of pages visited=2
> Number of rows qualified=10
> Number of rows visited=10
> Scan type=btree
> Tree height=2
> start position:
> >= on first 1 column(s).
> Ordered null semantics on the following columns:
> stop position:
> > on first 1 column(s).
> Ordered null semantics on the following columns:
> qualifiers:
> None
> optimizer estimated row count: 4.80
> optimizer estimated cost: 39.53
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