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From Julien Aymé (JIRA) <j...@apache.org>
Subject [jira] [Created] (CASSANDRA-6447) SELECT someColumns FROM table results in AssertionError in AbstractQueryPager.discardFirst
Date Wed, 04 Dec 2013 11:52:35 GMT
Julien Aymé created CASSANDRA-6447:
--------------------------------------

             Summary: SELECT someColumns FROM table results in AssertionError in AbstractQueryPager.discardFirst
                 Key: CASSANDRA-6447
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-6447
             Project: Cassandra
          Issue Type: Bug
          Components: Core
         Environment: Cluster: single node server (ubuntu)
Cassandra version: 2.0.3 (server/client)
Client: Datastax cassandra-driver-core 2.0.0-rc1
            Reporter: Julien Aymé


I have a query which must read all the rows from the table:
Query: "SELECT key, col1, col2, col3 FROM mytable"

Here is the corresponding code (this is using datastax driver):
{code}
ResultSet result = session.execute("SELECT key, col1, col2, col3 FROM mytable");
for (Row row : result) {
     // do some work with row
}
{code}

Messages sent from the client to Cassandra:
* 1st: {{QUERY SELECT key, col1, col2, col3 FROM mytable([cl=ONE, vals=[], skip=false, psize=5000,
state=null, serialCl=ONE])}}

* 2nd: {{QUERY SELECT key, col1, col2, col3 FROM mytable([cl=ONE, vals=[], skip=false, psize=5000,
state=java.nio.HeapByteBuffer[pos=24 lim=80 cap=410474], serialCl=ONE])}}

On the first message, everything is fine, and the server returns 5000 rows.
On the second message, paging is in progress, and the server fails in AbstractQueryPager.discardFirst:
AssertionError (stack trace attached).

Here is some more info (step by step debugging on reception of 2nd message):
{code}
AbstractQueryPager.fetchPage(int):
* pageSize=5000, currentPageSize=5001, rows size=5002, liveCount=5001
* containsPreviousLast(rows.get(0)) returns true

-> AbstractQueryPager.discardFirst(List<Row>):
* rows size=5002
* first=TreeMapBackedSortedColumns[with TreeMap size=1]

-> AbstractQueryPager.discardHead(ColumnFamily, ...):
* counter = ColumnCounter$GroupByPrefix
* iter.hasNext() returns true (TreeMap$ValueIterator with TreeMap size=1)
* Column c = DeletedColumn
* counter.count() -> c.isLive returns false (c is DeletedColumn)
* counter.live() = 0
* iter.hasNext() returns false
* Math.min(0, toDiscard==1) returns 0

<- AbstractQueryPager.discardFirst(List<Row>):
discarded = 0;
{code}
->  assert discarded == 1 *throws AssertionError*





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