Ben-Zvi commented on a change in pull request #1598: DRILL-6880: For Hash-Join
hash-table build - treat null keys as an equal match
URL: https://github.com/apache/drill/pull/1598#discussion_r245776838
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File path:
exec/java-exec/src/main/java/org/apache/drill/exec/physical/impl/common/HashTableTemplate.java
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@@ -224,6 +224,13 @@ private boolean isKeyMatch(int incomingRowIdx,
if (isProbe) {
match = isKeyMatchInternalProbe(incomingRowIdx, currentIdxWithinBatch);
} else {
+ // in case (of a hash-join only) where both the new incoming key and
the current are null, treat them as
+ // a match; i.e. the new would be added into the helper (but not the
Hash-Table !), though it would never
+ // be used (not putting it into the helper would take a bigger code
change, and some performance cost, hence
+ // not worth it). In the past such a new null key was added into the
Hash-Table (i.e., no match), which
+ // created long costly chains - SEE DRILL-6880)
+ if ( areBothKeysNull(incomingRowIdx, currentIdxWithinBatch) ) { return
true; }
Review comment:
The code on old line 230 is in a way "not clean", as it violates the
method's name/signature (which implies just a functional comparison of two
keys). That code advances to the next key in the hash-table chain in case of a
no-match. The "clean way" would be to make this code a separate
"advanceToNextIdx" method, which actually fits well in the for() loop where
_isKeyMatch()_ is used.
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