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https://issues.apache.org/jira/browse/DERBY-47?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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A B updated DERBY-47:
---------------------
Attachment: d47_mp_exec_v1.stat
d47_mp_exec_v1.patch
Committed d47_mp_codeGen_v1.patch with svn # 515795:
URL: http://svn.apache.org/viewvc?view=rev&rev=515795
And now attaching d47_mp_exec_v1.patch, which is a patch to implement
execution-time "probing" given a probe predicate "place-holder" and a list of
IN values. This patch creates a new execution-time result,
MuliProbeTableScanResultSet, to perform the probing. Generally speaking the
process is as follows, where "probe list" (aka "probeValues") corresponds to
the IN list in question.
0 - Open a scan using the first value in the (sorted) probe list as a start
AND stop key.
Then for each call to "getNextRowCore()":
1 - See if we have a row to read from the current scan position. If so,
return that row (done).
2 - If there are no more rows to read from the current scan position AND if
there are more
probe values to look at, then a) reopen the scan using the next probe value
as the start/
stop key and b) go back to step 1. Otherwise proceed to step 3.
3 - Return null (no more rows).
At a higher-level the changes in exec_v1.patch make it so that repeated calls
to MultiProbeTableScanResultSet.getNextRowCore() will first return all rows
matching probeValues[0], then all rows matching probeValues[1], and so on
(duplicate probe values are ignored). Once all matching rows for all values in
probeValues have been returned, the call to getNextRowCore() will return null,
thereby ending the scan.
In order to accommodate the above behavior, the following changes were made to
existing files:
1 - Add correct instantiation logic to the "getMultiProbeTableScanResultSet()"
method of GenericResultSetFactory, which was just a stub method before this
patch.
2 - Overloaded methods in TableScanResultSet to allow the passing of a "probe
value"
into the openScanController() and reopenScanController() methods. The
methods
then use the probe value (if one exists) as the start/stop key for
positioning
a scan, instead of using the start/stop key passed into the result set
constructor.
3 - Made the iapi.types.DataType class implement the java.lang.Comparable
interface
for the sake of easy sorting (just let the JVM do the sort). Since DataType
(the
superclass of all datatypes and base implementation of the
DataValueDescriptor
interface) already has a "compare()" method that returns an integer to
indicate
less than, greater than, or equal, all we have to do is wrap that method
inside
a "compareTo()" method and we're done.
There are two issues worth mentioning regarding this sort. First, the
compareTo()
method does not throw any exceptions, so if an error occurs while trying to
compare
two DataValueDescriptors, we will simply treat the values as "equal" when
running
in insane mode (in sane mode we will throw an assertion failure). Is this
acceptable? If not, is there a better way to handle this, aside from
writing my
own sorting code? (which is doable but seems like overkill).
Second, for some strange reason sorting the probeValues array directly (i.e.
in-place sort) leads to incorrect parameter value assignment when executing a
prepared statement multiple times. I was unable to figure out why that might
be (maybe related to DERBY-827?). To get around the problem I create clones
of the IN values and then sort the clones. That solves the problem but has
the obvious drawback of extra memory requirements. I'm hoping that for now
this is an okay workaround (progress, not perfection), but if anyone has any
ideas as to what could be going on here, I'd appreciate the input.
And of course, if there are any other reasons why it's bad to make DataType
implement the Comparable interface, I hope that reviewers can speak up. If
it comes down to it I can always add a simple sort method to MultiProbeTSCRS
and just use that.
As with all preceding patches, this patch should not have any functional effect
on Derby processing because the new behavior depends on probe predicates, which
do not yet exist. I have not yet had a chance to run derbyall as a sanity
check, but plan to do so before committing. In the meantime,
questions/comments/feedback on exec_v1.patch as attached would be much
appreciated.
> Some possible improvements to IN optimization
> ---------------------------------------------
>
> Key: DERBY-47
> URL: https://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
> Assigned To: A B
> Attachments: d47_engine_doNotCommit_v1.patch,
> d47_engine_doNotCommit_v1.stat, d47_mp_addlTestCases.patch,
> d47_mp_CBO_MoAP_v1.patch, d47_mp_CBO_MoAP_v1.stat, d47_mp_codeGen_v1.patch,
> d47_mp_codeGen_v1.stat, d47_mp_exec_v1.patch, d47_mp_exec_v1.stat,
> d47_mp_relOpPredCheck_v1.patch, d47_mp_relOpPredCheck_v1.stat,
> derby-47-performance-data.txt, derby-47-performance-data.txt,
> Derby47PerformanceTest.java, Derby47PerformanceTest.java,
> InListOperatorNode.java, QueryPlanUniqueIndexAndWordIndexOneTerm.txt,
> QueryPlanUniqueIndexAndWordIndexTwoTerms.txt,
> QueryPlanUniqueIndexOnlyOneTerm.txt, QueryPlanUniqueIndexOnlyTwoTerms.txt,
> readlocks.diff, readlocks_withContext.diff
>
>
> 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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