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https://issues.apache.org/jira/browse/CASSANDRA-9045?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14582508#comment-14582508
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Roman Tkachenko commented on CASSANDRA-9045:
--------------------------------------------
Hey guys.
So I implemented writes at EACH_QUORUM several weeks ago and has been
monitoring but it does not looks like it fixed the issue.
Check this out. I pulled the logs from both datacenters for one of reappeared
entries and correlated them with our repairs schedule. Reads (GETs) are done at
LOCAL_QUORUM.
{code}
Time DC RESULT
==========================================
2015-06-04T11:31:38 DC2 GET 200 --> record is present in both DCs
2015-06-04T15:25:01 DC1 GET 200
2015-06-04T19:24:06 DC1 DELETE 200 --> deleted in DC1
2015-06-04T19:45:16 DC2 GET 404 --> record disappeared from both DCs...
2015-06-05T07:10:32 DC1 GET 404
2015-06-05T10:16:28 DC2 GET 200 --> ... but somehow appeared back in
DC2 (no POST requests happened for this record)
2015-06-07T18:59:57 DC1 GET 404
2AM NODE IN DC2 REPAIR
4AM NODE IN DC1 REPAIR
2015-06-08T08:27:36 DC1 GET 200 --> record is present in both DCs
again, looks like DC2 "repaired" DC1
2015-06-09T15:29:50 DC2 GET 200
2015-06-09T16:05:30 DC1 DELETE 200
2015-06-09T16:05:30 DC1 GET 404
2015-06-09T21:08:24 DC2 GET 404
{code}
So the question is how the record managed to appear back in DC2... Do you have
any suggestions on how we can investigate this?
Thanks,
Roman
> Deleted columns are resurrected after repair in wide rows
> ---------------------------------------------------------
>
> Key: CASSANDRA-9045
> URL: https://issues.apache.org/jira/browse/CASSANDRA-9045
> Project: Cassandra
> Issue Type: Bug
> Components: Core
> Reporter: Roman Tkachenko
> Assignee: Marcus Eriksson
> Priority: Critical
> Fix For: 2.0.x
>
> Attachments: 9045-debug-tracing.txt, another.txt,
> apache-cassandra-2.0.13-SNAPSHOT.jar, cqlsh.txt, debug.txt, inconsistency.txt
>
>
> Hey guys,
> After almost a week of researching the issue and trying out multiple things
> with (almost) no luck I was suggested (on the user@cass list) to file a
> report here.
> h5. Setup
> Cassandra 2.0.13 (we had the issue with 2.0.10 as well and upgraded to see if
> it goes away)
> Multi datacenter 12+6 nodes cluster.
> h5. Schema
> {code}
> cqlsh> describe keyspace blackbook;
> CREATE KEYSPACE blackbook WITH replication = {
> 'class': 'NetworkTopologyStrategy',
> 'IAD': '3',
> 'ORD': '3'
> };
> USE blackbook;
> CREATE TABLE bounces (
> domainid text,
> address text,
> message text,
> "timestamp" bigint,
> PRIMARY KEY (domainid, address)
> ) WITH
> bloom_filter_fp_chance=0.100000 AND
> caching='KEYS_ONLY' AND
> comment='' AND
> dclocal_read_repair_chance=0.100000 AND
> gc_grace_seconds=864000 AND
> index_interval=128 AND
> read_repair_chance=0.000000 AND
> populate_io_cache_on_flush='false' AND
> default_time_to_live=0 AND
> speculative_retry='99.0PERCENTILE' AND
> memtable_flush_period_in_ms=0 AND
> compaction={'class': 'LeveledCompactionStrategy'} AND
> compression={'sstable_compression': 'LZ4Compressor'};
> {code}
> h5. Use case
> Each row (defined by a domainid) can have many many columns (bounce entries)
> so rows can get pretty wide. In practice, most of the rows are not that big
> but some of them contain hundreds of thousands and even millions of columns.
> Columns are not TTL'ed but can be deleted using the following CQL3 statement:
> {code}
> delete from bounces where domainid = 'domain.com' and address =
> '[email protected]';
> {code}
> All queries are performed using LOCAL_QUORUM CL.
> h5. Problem
> We weren't very diligent about running repairs on the cluster initially, but
> shorty after we started doing it we noticed that some of previously deleted
> columns (bounce entries) are there again, as if tombstones have disappeared.
> I have run this test multiple times via cqlsh, on the row of the customer who
> originally reported the issue:
> * delete an entry
> * verify it's not returned even with CL=ALL
> * run repair on nodes that own this row's key
> * the columns reappear and are returned even with CL=ALL
> I tried the same test on another row with much less data and everything was
> correctly deleted and didn't reappear after repair.
> h5. Other steps I've taken so far
> Made sure NTP is running on all servers and clocks are synchronized.
> Increased gc_grace_seconds to 100 days, ran full repair (on the affected
> keyspace) on all nodes, then changed it back to the default 10 days again.
> Didn't help.
> Performed one more test. Updated one of the resurrected columns, then deleted
> it and ran repair again. This time the updated version of the column
> reappeared.
> Finally, I noticed these log entries for the row in question:
> {code}
> INFO [ValidationExecutor:77] 2015-03-25 20:27:43,936
> CompactionController.java (line 192) Compacting large row
> blackbook/bounces:4ed558feba8a483733001d6a (279067683 bytes) incrementally
> {code}
> Figuring it may be related I bumped "in_memory_compaction_limit_in_mb" to
> 512MB so the row fits into it, deleted the entry and ran repair once again.
> The log entry for this row was gone and the columns didn't reappear.
> We have a lot of rows much larger than 512MB so can't increase this
> parameters forever, if that is the issue.
> Please let me know if you need more information on the case or if I can run
> more experiments.
> Thanks!
> Roman
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