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From "Bharath Vissapragada (Code Review)" <ger...@cloudera.org>
Subject [Impala-ASF-CR] [PREVIEW] IMPALA-5058: Improve concurrency of DDL/DML operations
Date Thu, 16 Nov 2017 06:11:31 GMT
Bharath Vissapragada has posted comments on this change. ( http://gerrit.cloudera.org:8080/8545
)

Change subject: [PREVIEW] IMPALA-5058: Improve concurrency of DDL/DML operations
......................................................................


Patch Set 1:

(1 comment)

http://gerrit.cloudera.org:8080/#/c/8545/1/fe/src/main/java/org/apache/impala/catalog/CatalogServiceCatalog.java
File fe/src/main/java/org/apache/impala/catalog/CatalogServiceCatalog.java:

http://gerrit.cloudera.org:8080/#/c/8545/1/fe/src/main/java/org/apache/impala/catalog/CatalogServiceCatalog.java@596
PS1, Line 596:       addTableToCatalogDeltaHelper(tbl, fromVersion, toVersion, resp);
Maybe I'm misunderstanding something but I still see the lock contention on 'tbl' here.

With the patch, given we don't lock the tables while snapshotting, there could be inflight
DDLs on tbl stuck in tryLockTable() (say CatalogOpEx.alterTable()) and that still holds the
tbl.lock_ and still hasn't updated tbl to a newer catalog version resulting in the if check
in L595 to pass. Eventually, that blocks on L622 stalling the getCatalogDelta() thread.


For example, we are trying to snapshot objects in (90, 100] and tbl's version is 95. We have
an alterTable() running on this particular table which got the new catalog version (say 105),
but hasn't still set it for the 'tbl' since it is waiting for the alter() to finish. All this
while, alter thread still holds the tbl.lock_, but the condition in L595 still passes with
this thread blocking on L622.

(My argument is based on my understanding is that 'tbl' still refers to the same table object
even after ImmutableList.copy() in L564)

Did I get something wrong?



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Gerrit-Project: Impala-ASF
Gerrit-Branch: master
Gerrit-MessageType: comment
Gerrit-Change-Id: I3032437f83d39bcc8cff14d897c7c106a4ab62d3
Gerrit-Change-Number: 8545
Gerrit-PatchSet: 1
Gerrit-Owner: Dimitris Tsirogiannis <dtsirogiannis@cloudera.com>
Gerrit-Reviewer: Alex Behm <alex.behm@cloudera.com>
Gerrit-Reviewer: Bharath Vissapragada <bharathv@cloudera.com>
Gerrit-Comment-Date: Thu, 16 Nov 2017 06:11:31 +0000
Gerrit-HasComments: Yes

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