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https://issues.apache.org/jira/browse/IMPALA-7564?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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bharath v updated IMPALA-7564:
------------------------------
Summary: Conservative FK/PK join type detection with complex equi-join
conjuncts (was: Conservative FK/PK join type estimation with complex equi-join
conjuncts)
> Conservative FK/PK join type detection with complex equi-join conjuncts
> -----------------------------------------------------------------------
>
> Key: IMPALA-7564
> URL: https://issues.apache.org/jira/browse/IMPALA-7564
> Project: IMPALA
> Issue Type: Bug
> Components: Frontend
> Affects Versions: Impala 2.12.0, Impala 2.13.0, Impala 3.1.0
> Reporter: bharath v
> Priority: Major
>
> With IMPALA-5547, we predict whether a join is an FK/PK join as follows.
> {noformat}
> // Iterate over all groups of conjuncts that belong to the same joined tuple
> id pair.
> // For each group, we compute the join NDV of the rhs slots and compare
> it to the
> // number of rows in the rhs table.
> for (List<EqJoinConjunctScanSlots> fkPkCandidate:
> scanSlotsByJoinedTids.values()) {
> double jointNdv = 1.0;
> for (EqJoinConjunctScanSlots slots: fkPkCandidate) jointNdv *=
> slots.rhsNdv();
> double rhsNumRows = fkPkCandidate.get(0).rhsNumRows();
> if (jointNdv >= Math.round(rhsNumRows * (1.0 -
> FK_PK_MAX_STATS_DELTA_PERC))) {
> // We cannot disprove that the RHS is a PK.
> if (result == null) result = Lists.newArrayList();
> result.addAll(fkPkCandidate);
> }
> }
> {noformat}
> We iterate through all the "simple" equi join conjuncts on the RHS, multiply
> their NDVs and check if it close to rhsNumRows. The issue here is that this
> can result in conservative FK/Pk detection if the equi-join conjuncts are not
> simple (of the form <slotRef> = <slotRef>)
> {noformat}
> /**
> * Returns a new EqJoinConjunctScanSlots for the given equi-join conjunct
> or null if
> * the given conjunct is not of the form <SlotRef> = <SlotRef> or if the
> underlying
> * table/column of at least one side is missing stats.
> */
> public static EqJoinConjunctScanSlots create(Expr eqJoinConjunct) {
> if (!Expr.IS_EQ_BINARY_PREDICATE.apply(eqJoinConjunct)) return null;
> SlotDescriptor lhsScanSlot =
> eqJoinConjunct.getChild(0).findSrcScanSlot();
> if (lhsScanSlot == null || !hasNumRowsAndNdvStats(lhsScanSlot)) return
> null;
> SlotDescriptor rhsScanSlot =
> eqJoinConjunct.getChild(1).findSrcScanSlot();
> {noformat}
> For example, the following query contains a complex equi-join conjunct
> {{substr(l.c3, 1, 6) = substr(r.c3, 1,6)}}, so while detecting if the left
> outer join is an FK/PK, we just check if
> {{NDVs(r.c1) * NDVs(r.c2) ~ r.numRows()}} which is incorrect.
> {noformat}
> [localhost:21000]> explain select * from test_left l left outer join
> test_right r on l.c1 = r.c1 and l.c2 = r.c2 and substr(l.c3, 1, 6) =
> substr(r.c3, 1,6);
> Query: explain select * from test_left l left outer join test_right r on l.c1
> = r.c1 and l.c2 = r.c2 and substr(l.c3, 1, 6) = substr(r.c3, 1,6)
> +-----------------------------------------------------------------------------------------+
> | Explain String
> |
> +-----------------------------------------------------------------------------------------+
> | Max Per-Host Resource Reservation: Memory=1.95MB Threads=5
> |
> | Per-Host Resource Estimates: Memory=66MB
> |
> |
> |
> | F02:PLAN FRAGMENT [UNPARTITIONED] hosts=1 instances=1
> |
> | | Per-Host Resources: mem-estimate=0B mem-reservation=0B
> thread-reservation=1 |
> | PLAN-ROOT SINK
> |
> | | mem-estimate=0B mem-reservation=0B thread-reservation=0
> |
> | |
> |
> | 04:EXCHANGE [UNPARTITIONED]
> |
> | | mem-estimate=0B mem-reservation=0B thread-reservation=0
> |
> | | tuple-ids=0,1N row-size=94B cardinality=49334767023
> |
> | | in pipelines: 00(GETNEXT)
> |
> | |
> |
> | F00:PLAN FRAGMENT [RANDOM] hosts=1 instances=1
> |
> | Per-Host Resources: mem-estimate=33.94MB mem-reservation=1.95MB
> thread-reservation=2 |
> | 02:HASH JOIN [LEFT OUTER JOIN, BROADCAST]
> |
> | | hash predicates: l.c1 = r.c1, l.c2 = r.c2, substr(l.c3, 1, 6) =
> substr(r.c3, 1, 6) |
> | | fk/pk conjuncts: none
> |
> | | mem-estimate=1.94MB mem-reservation=1.94MB spill-buffer=64.00KB
> thread-reservation=0 |
> | | tuple-ids=0,1N row-size=94B cardinality=49334767023
> |
> | | in pipelines: 00(GETNEXT), 01(OPEN)
> |
> | |
> |
> | |--03:EXCHANGE [BROADCAST]
> |
> | | | mem-estimate=0B mem-reservation=0B thread-reservation=0
> |
> | | | tuple-ids=1 row-size=47B cardinality=2510
> |
> | | | in pipelines: 01(GETNEXT)
> |
> | | |
> |
> | | F01:PLAN FRAGMENT [RANDOM] hosts=1 instances=1
> |
> | | Per-Host Resources: mem-estimate=32.00MB mem-reservation=8.00KB
> thread-reservation=2 |
> | | 01:SCAN HDFS [cdh72724.test_right r, RANDOM]
> |
> | | partitions=1/1 files=1 size=8B
> |
> | | stored statistics:
> |
> | | table: rows=2510 size=8B
> |
> | | columns: all
> |
> | | extrapolated-rows=disabled max-scan-range-rows=2510
> |
> | | mem-estimate=32.00MB mem-reservation=8.00KB thread-reservation=1
> |
> | | tuple-ids=1 row-size=47B cardinality=2510
> |
> | | in pipelines: 01(GETNEXT)
> |
> | |
> |
> | 00:SCAN HDFS [cdh72724.test_left l, RANDOM]
> |
> | partitions=1/1 files=1 size=8B
> |
> | stored statistics:
> |
> | table: rows=589658570 size=8B
> |
> | columns: all
> |
> | extrapolated-rows=disabled max-scan-range-rows=589658570
> |
> | mem-estimate=32.00MB mem-reservation=8.00KB thread-reservation=1
> |
> | tuple-ids=0 row-size=47B cardinality=589658570
> |
> | in pipelines: 00(GETNEXT)
> |
> +-----------------------------------------------------------------------------------------+
> Fetched 48 row(s) in 0.02s
> {noformat}
> We should either consider NDVs of complex conjuncts (error-prone for obvious
> reasons) or generally assume a join to be FK/PK until and unless proven
> otherwise.
> Here is the plan if the complex conjunct is relaxed to a simple <slotRef> =
> <slotRef> type. We can see that it detects the join to be of fk/pk type.
> {noformat}
> [localhost:21000] cdh72724> explain select * from test_left l left outer join
> test_right r on l.c1 = r.c1 and l.c2 = r.c2 and l.c3 = r.c3;
> Query: explain select * from test_left l left outer join test_right r on l.c1
> = r.c1 and l.c2 = r.c2 and l.c3 = r.c3
> +-----------------------------------------------------------------------------------------+
> | Explain String
> |
> +-----------------------------------------------------------------------------------------+
> | Max Per-Host Resource Reservation: Memory=1.95MB Threads=5
> |
> | Per-Host Resource Estimates: Memory=66MB
> |
> |
> |
> | F02:PLAN FRAGMENT [UNPARTITIONED] hosts=1 instances=1
> |
> | | Per-Host Resources: mem-estimate=0B mem-reservation=0B
> thread-reservation=1 |
> | PLAN-ROOT SINK
> |
> | | mem-estimate=0B mem-reservation=0B thread-reservation=0
> |
> | |
> |
> | 04:EXCHANGE [UNPARTITIONED]
> |
> | | mem-estimate=0B mem-reservation=0B thread-reservation=0
> |
> | | tuple-ids=0,1N row-size=94B cardinality=589658570
> |
> | | in pipelines: 00(GETNEXT)
> |
> | |
> |
> | F00:PLAN FRAGMENT [RANDOM] hosts=1 instances=1
> |
> | Per-Host Resources: mem-estimate=33.94MB mem-reservation=1.95MB
> thread-reservation=2 |
> | 02:HASH JOIN [LEFT OUTER JOIN, BROADCAST]
> |
> | | hash predicates: l.c1 = r.c1, l.c2 = r.c2, l.c3 = r.c3
> |
> | | fk/pk conjuncts: l.c1 = r.c1, l.c2 = r.c2, l.c3 = r.c3
> |
> | | mem-estimate=1.94MB mem-reservation=1.94MB spill-buffer=64.00KB
> thread-reservation=0 |
> | | tuple-ids=0,1N row-size=94B cardinality=589658570
> |
> | | in pipelines: 00(GETNEXT), 01(OPEN)
> |
> | |
> |
> | |--03:EXCHANGE [BROADCAST]
> |
> | | | mem-estimate=0B mem-reservation=0B thread-reservation=0
> |
> | | | tuple-ids=1 row-size=47B cardinality=2510
> |
> | | | in pipelines: 01(GETNEXT)
> |
> | | |
> |
> | | F01:PLAN FRAGMENT [RANDOM] hosts=1 instances=1
> |
> | | Per-Host Resources: mem-estimate=32.00MB mem-reservation=8.00KB
> thread-reservation=2 |
> | | 01:SCAN HDFS [cdh72724.test_right r, RANDOM]
> |
> | | partitions=1/1 files=1 size=8B
> |
> | | stored statistics:
> |
> | | table: rows=2510 size=8B
> |
> | | columns: all
> |
> | | extrapolated-rows=disabled max-scan-range-rows=2510
> |
> | | mem-estimate=32.00MB mem-reservation=8.00KB thread-reservation=1
> |
> | | tuple-ids=1 row-size=47B cardinality=2510
> |
> | | in pipelines: 01(GETNEXT)
> |
> | |
> |
> | 00:SCAN HDFS [cdh72724.test_left l, RANDOM]
> |
> | partitions=1/1 files=1 size=8B
> |
> | stored statistics:
> |
> | table: rows=589658570 size=8B
> |
> | columns: all
> |
> | extrapolated-rows=disabled max-scan-range-rows=589658570
> |
> | mem-estimate=32.00MB mem-reservation=8.00KB thread-reservation=1
> |
> | tuple-ids=0 row-size=47B cardinality=589658570
> |
> | in pipelines: 00(GETNEXT)
> |
> +-----------------------------------------------------------------------------------------+
> Fetched 48 row(s) in 0.01s
> {noformat}
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