[jira] [Created] (IMPALA-10468) DROP events which are generated while a batch is being processed may add table incorrectly

["Vihang Karajgaonkar (Jira)" <ji...@apache.org>]

Vihang Karajgaonkar created IMPALA-10468:
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             Summary: DROP events which are generated while a batch is being processed may add table incorrectly
                 Key: IMPALA-10468
                 URL: https://issues.apache.org/jira/browse/IMPALA-10468
             Project: IMPALA
          Issue Type: Improvement
            Reporter: Vihang Karajgaonkar
            Assignee: Vihang Karajgaonkar


One of the problems with CREATE/DROP events is that they may occur while a batch is being processed and hence EventsProcessor may not able aware of that.

For example, consider the following sequence of statements:

create table foo (c1 int);
drop table foo;
create table foo (c2 int);
drop table foo;

These statements will generate CREATE_TABLE, DROP_TABLE,  CREATE_TABLE, DROP_TABLE event sequence. Generally, if all these 4 events are fetched in a batch, then the first CREATE_TABLE and third CREATE_TABLE is ignored because it is followed by the a DROP_TABLE in the sequence and the DROP_TABLE events take no effect since the table doesn't exist in catalogd anymore.

However, if the events processor fetches these events in 2 batches (3 and 1) then after the first batch of CREATE_TABLE, DROP_TABLE,  CREATE_TABLE is processed, the third event will add the table foo in the catalogd. The subsequent batch's DROP_TABLE will be processed and remove the table, but between the two batches, catalogd will say that a table called foo exists. This can lead to statements getting errored out. Eg. a statement like create table foo (c3 int) after the above statements will error out with a TableAlreadyExists error.

The problem happens for databases too. So far I have not been able to reproduce this for Partitions but I don't see why it will not happen with Partitions also.




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