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From "Andrew Hust (JIRA)" <>
Subject [jira] [Updated] (CASSANDRA-10250) Executing lots of schema alters concurrently can lead to dropped alters
Date Wed, 02 Sep 2015 04:23:45 GMT


Andrew Hust updated CASSANDRA-10250:
    Attachment: node3.log

> Executing lots of schema alters concurrently can lead to dropped alters
> -----------------------------------------------------------------------
>                 Key: CASSANDRA-10250
>                 URL:
>             Project: Cassandra
>          Issue Type: Bug
>            Reporter: Andrew Hust
>         Attachments:, node1.log, node2.log, node3.log
> A recently added [dtest|]
has been flapping on cassci and has exposed an issue with running lots of schema alterations
concurrently.  The failures occur on healthy clusters but seem to occur at higher rates when
1 node is down during the alters.
> The test executes the following – 440 total commands:
> -	Create 20 new tables
> -	Drop 7 columns one at time across 20 tables
> -	Add 7 columns on at time across 20 tables
> -	Add one column index on each of the 7 columns on 20 tables
> Outcome is random. Majority of the failures are dropped columns still being present,
but new columns and indexes have been observed to be incorrect.  The logs are don’t have
exceptions and the columns/indexes that are incorrect don’t seem to follow a pattern.  Running
a {{nodetool describecluster}} on each node shows the same schema id on all nodes.
> Attached is a python script extracted from the dtest.  Running against a local 3 node
cluster will reproduce the issue (with enough runs – fails ~20% on my machine).
> Also attached is the node logs from a run with when a dropped column (alter_me_7 table,
column s1) is still present.  Checking the system_schema tables for this case shows the s1
column in both the columns and drop_columns tables.
> This has been flapping on cassci on versions 2+ and doesn’t seem to be related to changes
in 3.0.  More testing needs to be done though.

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