Hi All,
I have a table which has one column per user. It revives at lot of updates
to these columns through out the life time. They are always updates on a
few specific columns Firstly is Cassandra storing a Tombstone for each of
these old column values.
I have run a simple select and seen the following tracing results:
activity
| timestamp | source | source_elapsed
-------------------------------------------------------------------------------------------+--------------+-----------+----------------
execute_cql3_query | 19:48:36,582 | 127.0.0.1 | 0
Parsing SELECT Account, Balance FROM AccountBalances WHERE Account =
'test9' LIMIT 10000; | 19:48:36,582 | 127.0.0.1 | 56
Preparing statement | 19:48:36,582 | 127.0.0.1 | 181
Executing single-partition query on accountbalances | 19:48:36,583 |
127.0.0.1 | 878
Acquiring sstable references | 19:48:36,583 | 127.0.0.1 | 895
Merging memtable tombstones | 19:48:36,583 | 127.0.0.1 | 918
Key cache hit for sstable 569 | 19:48:36,583 | 127.0.0.1 | 997
Seeking to partition beginning in data file | 19:48:36,583 | 127.0.0.1 |
1034
Skipped 0/1 non-slice-intersecting sstables, included 0 due to tombstones |
19:48:36,583 | 127.0.0.1 | 1383
Merging data from memtables and 1 sstables | 19:48:36,583 | 127.0.0.1 |
1402
Read 1 live and 123780 tombstoned cells | 19:48:36,710 | 127.0.0.1 |
128631
Request complete | 19:48:36,711 | 127.0.0.1 | 129276
As you can see that's awful lot of tombstoned cells. That's after a full
compaction as well. Just so you are aware this table is updated using a
Paxos IF statement.
Its still seems fairly snappy however I am concerned its only going to get
worse.
Would I better off adding a time based key to the primary key. Then doing a
sepperate insert and then deleting the original. If I did the query with a
limit of one it should always find the first rows before hitting a
tombstone. Is that correct?
Thanks,
Charlie M
