cassandra-commits mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "Paulo Motta (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-11500) Obsolete MV entry may not be properly deleted
Date Tue, 05 Sep 2017 07:56:00 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-11500?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16153239#comment-16153239
] 

Paulo Motta commented on CASSANDRA-11500:
-----------------------------------------

bq. As we discussed offline, we need to make sure the raw data including tombstone, expired
liveness are shipped to the coordinator side. Enforcing strict liveness in ReadCommand.executeLocally()
would remove the row before digest or data response. Instead, we add enforceStrictLiveness
to Row.purge to get the same result but less interfaces changes for Row.

Excellent catch, my bad for overlooking this, but gladly you added a new dtest for it: [test_base_column_in_view_pk_complex_timestamp_with_flush|https://github.com/apache/cassandra-dtest/commit/6d77ace5361f020ba182072ade9f4ab98025c213#diff-62ba429edee6a4681782f078246c9893R993].
Enforcing strict liveness during reconciliation on the coordinator is the correct approach
to differentiate between non-existing and removed rows via strict liveness. Ideally strict
liveness would be a row property but as we saw in the previous version, this requires changes
a bunch of other classes and interfaces, so let's keep it as a flag to Row.purge for now.

bq. Shadowable tombstone will be deprecated and use expired livenessInfo if the deletion time
is greater than merged-row deletion to avoid uncessary expired livenessInfo.

LGTM, this will prevent using expired liveness info in most cases. We should probably remove
this as part of CASSANDRA-13826 since we're overlading ExpiringLivenessInfo for a different
purpose but it should be fine for now.

Final patch and CI results look good and I'm confident we've exercised all edge cases properly
with unit and dtests. Committed dtests to master as {{6d77ace5361f020ba182072ade9f4ab98025c213}}.
Commited to cassandra-3.0 branch as {{1b36740ebe66b8ed4c3d6cb64eb2419a9279dfbf}} and merged
up to cassandra-3.11 and trunk. Great job Zhao!

*Summary of improvements and fixed issues*

This patch address most outstanding timestamp problems with MVs on the 3.x series without
changing the binary or storage protocol. The remaining issues which requires storage engine
and binary protocol changes will be addressed on CASSANDRA-13826 on trunk. Below is a summary
of the main changes and fixes this patch introduces.

{noformat}
* View same PK components as base

* DELETE of selected column should not affect out of order updates (testPartialDeleteSelectedColumn)
* DELETE of unselected column/collection should not affect ordered updates (testUpdateColumnNotInView,
testPartialUpdateWithUnselectedCollections - CASSANDRA-13127)
* Unselected columns should keep view row alive when other columns expire (testUnselectedColumnsTTL
- CASSANDRA-13127)

* Extra column on view PK

* View row should expire when view PK column expires in base (testUpdateColumnInViewPKWithTTL
- CASSANDRA-13657)
* Commutative row deletion (testCommutativeRowDeletion, testCellTombstoneAndShadowableTombstones
- CASSANDRA-13409)
* Out of order updates to extra column on view PK (testUpdateWithColumnTimestampBiggerThanPk,
testUpdateWithColumnTimestampSmallerThanPk, CASSANDRA-11500)

* Unsupported scenarios

* DELETE of unselected column should not affect out of order updates (testPartialDeleteUnselectedColumn
- CASSANDRA-13127 - Added )
* Filtering by non-PK base column (Only on C* 3.11+, disallowed on CASSANDRA-13798)

* Additional MV tests

* testNonBaseColumnInViewPk
* testRangeDeletion
* testStrictLivenessTombstone
* testFrozenCollectionsWithComplexInnerType
* testMVWithDifferentColumns
* testBaseTTLWithSameTimestampTest
{noformat}

*Summary of code changes*

{noformat}
1. Using expired livenessInfo if computed deletion time is greater than merged row deletion.
There are only 2 cases:
      a. non-pk base column used in view pk is removed by partial update or partial delete
      b. unselected base column is removed by partial update or partial delete
   
   Current shadowable tombstone is not used to avoid the issue of resurrecting deleted cells
(CASSANDRA-13049). We will expired-livenessInfo and merged base row deletion instead.

2. It's strict-liveness iff there is non-key base column in view-pk. The existence of view
row is solely base on this non-key base column.

3. If there is no non-base PK column in view-pk, the view's liveness/deletion is using max
of base livenessIno + unselected column. unselected column's ttl is used only when it affects
view row liveness. Selected columns won't contribute to livenessInfo or row deletion.
    * this wouldn't support complex cases as explained above. eg. c/d unselected, update c@10,
delete c@11, update d@5. view row should be alive but dead - We added a note to NEWS.txt as
well as documentation about this unsupported case.
    * since we change the way the deletion timestamp is computed in this case, an older deletion
to the non-base PK may not properly shadow a previous view row with a greater timestamp, so
repair should be run before upgrade on the base table to ensure deletions are properly generated
with the previous approach, or alternatively repair can be run on the views after upgrade
(added note to NEWS.txt).

4. in TableViews.java, the DeletionTracker should be applied even if existing has no data,
eg. partition-deletion

5. When generating read command to read existing base data, need to query all base columns
instead of view's queried column if base and view having same key columns to read unselected
column.

6. Fix handling of timestamp tie on PrimaryKeyLivenessInfo to match the one for cell resolution:
on timestamp tie, greater timestamp supersede lower timestamp and TTL supersedes non-TTL (tested
on testBaseTTLWithSameTimestampTest).

7. Disallow drop of columns on base tables with MVs because we cannot tell if the dropped
column is keeping a view row alive (will be fixed on CASSANDRA-13826)
{noformat}

> Obsolete MV entry may not be properly deleted
> ---------------------------------------------
>
>                 Key: CASSANDRA-11500
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-11500
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Materialized Views
>            Reporter: Sylvain Lebresne
>            Assignee: ZhaoYang
>             Fix For: 3.0.15, 3.11.1, 4.0
>
>
> When a Materialized View uses a non-PK base table column in its PK, if an update changes
that column value, we add the new view entry and remove the old one. When doing that removal,
the current code uses the same timestamp than for the liveness info of the new entry, which
is the max timestamp for any columns participating to the view PK. This is not correct for
the deletion as the old view entry could have other columns with higher timestamp which won't
be deleted as can easily shown by the failing of the following test:
> {noformat}
> CREATE TABLE t (k int PRIMARY KEY, a int, b int);
> CREATE MATERIALIZED VIEW mv AS SELECT * FROM t WHERE k IS NOT NULL AND a IS NOT NULL
PRIMARY KEY (k, a);
> INSERT INTO t(k, a, b) VALUES (1, 1, 1) USING TIMESTAMP 0;
> UPDATE t USING TIMESTAMP 4 SET b = 2 WHERE k = 1;
> UPDATE t USING TIMESTAMP 2 SET a = 2 WHERE k = 1;
> SELECT * FROM mv WHERE k = 1; // This currently return 2 entries, the old (invalid) and
the new one
> {noformat}
> So the correct timestamp to use for the deletion is the biggest timestamp in the old
view entry (which we know since we read the pre-existing base row), and that is what CASSANDRA-11475
does (the test above thus doesn't fail on that branch).
> Unfortunately, even then we can still have problems if further updates requires us to
overide the old entry. Consider the following case:
> {noformat}
> CREATE TABLE t (k int PRIMARY KEY, a int, b int);
> CREATE MATERIALIZED VIEW mv AS SELECT * FROM t WHERE k IS NOT NULL AND a IS NOT NULL
PRIMARY KEY (k, a);
> INSERT INTO t(k, a, b) VALUES (1, 1, 1) USING TIMESTAMP 0;
> UPDATE t USING TIMESTAMP 10 SET b = 2 WHERE k = 1;
> UPDATE t USING TIMESTAMP 2 SET a = 2 WHERE k = 1; // This will delete the entry for a=1
with timestamp 10
> UPDATE t USING TIMESTAMP 3 SET a = 1 WHERE k = 1; // This needs to re-insert an entry
for a=1 but shouldn't be deleted by the prior deletion
> UPDATE t USING TIMESTAMP 4 SET a = 2 WHERE k = 1; // ... and we can play this game more
than once
> UPDATE t USING TIMESTAMP 5 SET a = 1 WHERE k = 1;
> ...
> {noformat}
> In a way, this is saying that the "shadowable" deletion mechanism is not general enough:
we need to be able to re-insert an entry when a prior one had been deleted before, but we
can't rely on timestamps being strictly bigger on the re-insert. In that sense, this can be
though as a similar problem than CASSANDRA-10965, though the solution there of a single flag
is not enough since we can have to replace more than once.
> I think the proper solution would be to ship enough information to always be able to
decide when a view deletion is shadowed. Which means that both liveness info (for updates)
and shadowable deletion would need to ship the timestamp of any base table column that is
part the view PK (so {{a}} in the example below).  It's doable (and not that hard really),
but it does require a change to the sstable and intra-node protocol, which makes this a bit
painful right now.
> But I'll also note that as CASSANDRA-1096 shows, the timestamp is not even enough since
on equal timestamp the value can be the deciding factor. So in theory we'd have to ship the
value of those columns (in the case of a deletion at least since we have it in the view PK
for updates). That said, on that last problem, my preference would be that we start prioritizing
CASSANDRA-6123 seriously so we don't have to care about conflicting timestamp anymore, which
would make this problem go away.



--
This message was sent by Atlassian JIRA
(v6.4.14#64029)

---------------------------------------------------------------------
To unsubscribe, e-mail: commits-unsubscribe@cassandra.apache.org
For additional commands, e-mail: commits-help@cassandra.apache.org


Mime
View raw message