[jira] [Created] (CASSANDRA-6407) CQLSH hangs forever when querying more than certain amount of data

["Nikolai Grigoriev (JIRA)" <ji...@apache.org>]

Nikolai Grigoriev created CASSANDRA-6407:
--------------------------------------------

             Summary: CQLSH hangs forever when querying more than certain amount of data
                 Key: CASSANDRA-6407
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-6407
             Project: Cassandra
          Issue Type: Bug
          Components: Tools
         Environment: Oracle Linux 6.4, JDK 1.7.0_25-b15, Cassandra 2.0.2
            Reporter: Nikolai Grigoriev


I have a table like this (slightly simplified for clarity):

{code}
CREATE TABLE my_test_table (
		uid  uuid,
		d_id	 uuid,
		a_id	 uuid,	
		c_id	text,
		i_id	blob,	
		data	text,
		PRIMARY KEY ((uid, d_id, a_id), c_id, i_id)
);
{code}

I have created about over a hundred (117 to be specific) of sample entities with the same row key and different clustering keys. Each has a blob of approximately 4Kb.

I have tried to fetch all of them with a query like this via CQLSH:

{code}
select * from my_test_table where uid=44338526-7aac-4640-bcde-0f4663c07572 and a_id=00000000-0000-4000-0000-000000000002 and d_id=00000000-0000-1e64-0000-000000000001 and c_id='list-2'
{code}

This query simply hangs in CQLSH, it does not return at all until I abort it.

Then I started playing with LIMIT clause and found that this query returns instantly (with good data) when I use LIMIT 55 but hangs forever when I use LIMIT 56.

Then I tried to just query all "i_id" values like this:

{code}
select i_id from my_test_table where uid=44338526-7aac-4640-bcde-0f4663c07572 and a_id=00000000-0000-4000-0000-000000000002 and d_id=00000000-0000-1e64-0000-000000000001 and c_id='list-2'
{code}

And this query returns instantly with the complete set of 117 values. So I started thinking that it must be something about the total size of the response, not the number of results or the number of columns to be fetches in slices. And I have tried another test:

{code}
select cdata from my_test_table where uid=44338526-7aac-4640-bcde-0f4663c07572 and a_id=00000000-0000-4000-0000-000000000002 and d_id=00000000-0000-1e64-0000-000000000001 and c_id='list-2' LIMIT 63
{code}

This query returns instantly but if I change the limit to 64 it hangs forever. Since my blob is about 4Kb for each entity it *seems* like the query hangs when the total size of the response exceeds 252..256Kb. Looks quite suspicious especially because 256Kb is such a particular number. I am wondering if this has something to do with the result paging.

I did not test if the issue is reproducible outside of CQLSH but I do recall that I observed somewhat similar behavior when fetching relatively large data sets.

I can consistently reproduce this problem on my cluster. I am also attaching the jstack output that I have captured when CQLSH was hanging on one of these queries.



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