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From "Alberto Pujante (JIRA)" <j...@apache.org>
Subject [jira] [Created] (CASSANDRA-5721) Extremely slow reads after flusing with a single row with few columns
Date Wed, 03 Jul 2013 16:54:20 GMT
Alberto Pujante created CASSANDRA-5721:
------------------------------------------

             Summary: Extremely slow reads after flusing with a single row with few columns
                 Key: CASSANDRA-5721
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-5721
             Project: Cassandra
          Issue Type: Bug
          Components: Core
         Environment: Ubuntu 32 bits, windows xp
            Reporter: Alberto Pujante


I don't know if this is a bug or a normal behaviour. After doing some insertions and deletions
(new keyspace, new table) and make a flush of the table, Cassandra gives extremely slow reads
(and finally timeouts).  Compactions  also are extremely slow (with only a hundred of columns).


I've created a example script to test this. The result table of the output script has 750
live columns and 750 tombstones and only is flushed one memtable.
When I don't do deletions and I read the entire row, Cassandra gives normal times. In this
case it would be best for performance manually mark columns as deleted and when row reaches
a % of deletes copy "no deleted columns" in a new row and delete the old one( row deletion).

Even in models with a few columns deletions, after a while Cassandra would become  extremely
slow, and compactions would be very painfull

    public void test() throws InterruptedException {
        session.execute("CREATE KEYSPACE ks WITH replication " + "="
                + "{'class':'SimpleStrategy', 'replication_factor':1};");
        session.execute("use ks;");
        //session.execute("drop table timelineTable;");
        session.execute("CREATE " + "TABLE ks.timelineTable ("
                + "key blob,"
                + "timeline timestamp,"
                + "value blob,"
                + "PRIMARY KEY (key, timeline)"
                + ") WITH CLUSTERING ORDER BY (timeline DESC) and gc_grace_seconds=0;");

        Long interval;
        Long time = new Date().getTime();
        int j = 0;
        while (j < 15) {
            int i = 0;
            interval = new Date().getTime();
            while (i < 100) {
                session.execute("insert into timelineTable (key,timeline,value) values (0x01,"
                        + time.toString() + ",0x0" + Integer.toHexString(j) + ")");
                time++;
                i++;
            }
            System.out.println("Insert Interval:" + (new Date().getTime() - interval));

            interval = new Date().getTime();
            ResultSet results = session.execute("SELECT * FROM timelineTable"
                    + " WHERE key = 0x01 ORDER BY timeline DESC limit 100");
            System.out.println("Read Interval:" + (new Date().getTime() - interval));

            i = 0;
            interval = new Date().getTime();
            for (Row row : results) {
                if (i >= 50) {
                    session.execute("DELETE FROM timelineTable WHERE key = 0x01 AND timeline="
                            + row.getDate("timeline").getTime());
                }
                i++;
            }
            System.out.println("Delete Interval:" + (new Date().getTime() - interval));
            j++;
            System.out.println("");
        }
    }

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