[ http://issues.apache.org/jira/browse/DERBY-805?page=all ]
A B updated DERBY-805:
----------------------
Attachment: DERBY-805_v4.html
d805_phase4_v1.patch
d805_phase4_v1.stat
Attaching two things to this issue:
1 - DERBY-805_v4.html: an updated document that includes a description of my
proposed changes for Phase 4. See "Section VII".
2 - d805_phase4_v1.patch: a patch that implements the Phase 4 changes described
in Section VII of the _v4.html document.
The phase4_v1 patch also fixes a small error in BaseTableNumberVisitor.java and
updates the lang/predicatePushdown.sql test to account for the new Phase 4
behavior. As part of the changes for predicatePushdown.sql I have added a lot
more data to the tables, which means the test queries take longer to run. So
where this test used to run in under a minute on my machine, it now takes over
4 minutes to complete. That's expected given my changes, but I thought I
should state that explicitly in case anyone notices.
I ran derbyall on Linux Redhat using sane jars with IBM 1.4.2 and saw no new
failures. I also ran the updated lang/predicatePushdown.sql test against IBM
wsdd5.6 and Sun 1.5 and the test passed without problems.
If anyone has time to review and commit, that would be great. Note that while
the patch is around 5500 lines, only about 600 lines of it are actual code
changes; the rest is the result of the updated predicatePushdown.sql test and
the corresponding output (a lot of query plans are printed in this test, so the
output is quite large).
> Push join predicates into union and other set operations. DERBY-649
> implemented scalar (single table) predicate pushdown. Adding join predicate
> push down could improve performance significantly.
> --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
>
> Key: DERBY-805
> URL: http://issues.apache.org/jira/browse/DERBY-805
> Project: Derby
> Type: Sub-task
> Components: SQL
> Versions: 10.1.2.0, 10.2.0.0
> Environment: generic
> Reporter: Satheesh Bandaram
> Assignee: A B
> Fix For: 10.2.0.0
> Attachments: DERBY-805.html, DERBY-805_v2.html, DERBY-805_v3.html,
> DERBY-805_v4.html, d805_phase1_v1.patch, d805_phase1_v1.stat,
> d805_phase1_v2.patch, d805_phase1_v2.stat, d805_phase1_v3.patch,
> d805_phase1_v3.stat, d805_phase2_v1.patch, d805_phase2_v1.stat,
> d805_phase3_v1.patch, d805_phase3_v1.stat, d805_phase4_v1.patch,
> d805_phase4_v1.stat, phase2_javadocFix.patch, predPushdown_testFix.patch
>
> Fix for DERBY-649 implemented scalar (single table) predicate push down into
> UNIONs. While this improves performance for one set of queries, ability to
> push join-predicates further improves Derby performance by enabling use of
> indices where possible.
> For example,
> create view V1 as select i, j from T1 union all select i,j from T2;
> create view V2 as select a,b from T3 union all select a,b from T4;
> insert into T1 values (1,1), (2,2), (3,3), (4,4), (5,5);
> For a query like
> select * from V1, V2 where V1.j = V2.b and V1.i =1;
> If the join order choosen is V1,V2, V1 can use index on V1.i (if present)
> following fix for DERBY-649. But if there is a index on V2.b also, Derby
> currently can't use that index. By pushing join predicate, Derby would be
> able to use the index and improve performance. Some of the queries I have
> seen (not the one shown here...) could improve from 70-120 seconds to about
> one second.
> Note there is a good comment by Jeff Lichtman about join-predicate push down.
> I am copying parts of it here for completeness of this report: (Modified)
> If predicate push down is done during optimization, it would be possible to
> push joins into the union as long as it's in the right place in the join
> order.
> For example:
> create view v as select * from t1 union all select * from t2;
> select * from v, t3 where v.c1 = t3.c2;
> In this select, if t3 is the outer table then the qualification could be
> pushed into the union and optimized there, but if t3 is the inner table the
> qualification can't be pushed into the union.
> If the pushing is done at preprocess time (i.e. before optimization) it is
> impossible to know whether a join qualification like this can be safely
> pushed.
> There's a comment in UnionNode.optimizeIt() saying:
> /* RESOLVE - don't try to push predicated through for now */
> This is where I'd expect to see something for pushing predicates into the
> union during optimization.
> BTW, the business of pushing and pulling predicates during optimization can
> be hard to understand and debug, so maybe it's best to only handle the simple
> cases and do it during preprocessing.
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