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From "Benjamin Lerer (JIRA)" <j...@apache.org>
Subject [jira] [Reopened] (CASSANDRA-11314) Inconsistent select count(*)
Date Thu, 10 Mar 2016 08:52:40 GMT

     [ https://issues.apache.org/jira/browse/CASSANDRA-11314?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Benjamin Lerer reopened CASSANDRA-11314:
----------------------------------------

[~mlemnaru] I just would like to double check the problem. Some stuff seems weird to me. I
just want to take the time to properly look into the problem.
It is better to double check and find nothing than to miss a real problem that can hit people
once they are in production. :-)

> Inconsistent select count(*)
> ----------------------------
>
>                 Key: CASSANDRA-11314
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-11314
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Local Write-Read Paths
>         Environment: Ununtu 14.04 LTS
>            Reporter: Mircea Lemnaru
>            Assignee: Benjamin Lerer
>         Attachments: testrun.log, vnodes_and_hosts
>
>
> Hello,
> I currently have this setup: 
> Cassandra 3.3 (Community edition downloaded from Datastax) installed on 3 nodes and I
have created this table:
> CREATE TABLE billing.collected_data_day (
>     collection_day int,
>     timestamp timestamp,
>     record_id uuid,
>     dimensions map<text, text>,
>     entity_id text,
>     measurements map<text, text>,
>     source_id text,
>     PRIMARY KEY (collection_day, timestamp, record_id)
> ) WITH CLUSTERING ORDER BY (timestamp ASC, record_id ASC)
>     AND bloom_filter_fp_chance = 0.01
>     AND caching = {'keys': 'ALL', 'rows_per_partition': 'NONE'}
>     AND comment = ''
>     AND compaction = {'class': 'org.apache.cassandra.db.compaction.SizeTieredCompactionStrategy',
'max_threshold': '32', 'min_threshold': '4'}
>     AND compression = {'chunk_length_in_kb': '64', 'class': 'org.apache.cassandra.io.compress.LZ4Compressor'}
>     AND crc_check_chance = 1.0
>     AND dclocal_read_repair_chance = 0.1
>     AND default_time_to_live = 0
>     AND gc_grace_seconds = 864000
>     AND max_index_interval = 2048
>     AND memtable_flush_period_in_ms = 0
>     AND min_index_interval = 128
>     AND read_repair_chance = 0.0
>     AND speculative_retry = '99PERCENTILE';
> This table as you notice is partitioned by collection_day. This is because at the end
of the day we need to have fast access to all the data generated in a day. collection day
will be the x day from 1970
> In this table we have inserted roughly 12milion rows for testing purposes and we did
a simple count. As you can see the results vary ... 
> cqlsh:billing> select count(*) from collected_data_day where collection_day=16462;
>  count
> -------
>  55341
> (1 rows)
> cqlsh:billing> select count(*) from collected_data_day where collection_day=16462;
>  count
> -------
>  55372
> (1 rows)
> cqlsh:billing> select count(*) from collected_data_day where collection_day=16462;
>  count
> -------
>  55300
> (1 rows)
> cqlsh:billing> select count(*) from collected_data_day where collection_day=16462;
>  count
> -------
>  55300
> (1 rows)
> cqlsh:billing> select count(*) from collected_data_day where collection_day=16462;
>  count
> -------
>  55300
> (1 rows)
> cqlsh:billing> select count(*) from collected_data_day where collection_day=16462;
>  count
> -------
>  55303
> (1 rows)
> cqlsh:billing> select count(*) from collected_data_day where collection_day=16462;
>  count
> -------
>  55374
> (1 rows)
> I am running the query from the seed node of the cassandra cluster. As you can see most
of the results are varying and I don't know the reason for this. We are not writing anything
into the cluster at this time , we are only querying the cluster and only using this CQLSH.
> This is very similar to CASSANDRA-8940 but that is targeted for 2.1x
> Could it be that we are having the same issue in 3.3 ? 
> Please let me know what extra info I can provide



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