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From mcasandra <mohitanch...@gmail.com>
Subject flush_largest_memtables_at messages in 7.4
Date Tue, 12 Apr 2011 18:36:14 GMT
I am using cassandra 7.4 and getting these messages.

Heap is 0.7802529021498031 full. You may need to reduce memtable and/or
cache sizes Cassandra will now flush up to the two largest memtables to free
up memory. Adjust flush_largest_memtables_at threshold in cassandra.yaml if
you don't want Cassandra to do this automatically

How do I verify that I need to adjust any thresholds? And how to calculate
correct value?

When I got this message only reads were occuring.

create keyspace StressKeyspace
    with replication_factor = 3
    and placement_strategy = 'org.apache.cassandra.locator.SimpleStrategy';

use StressKeyspace;
drop column family StressStandard;
create column family StressStandard
    with comparator = UTF8Type
    and keys_cached = 1000000
    and memtable_flush_after = 1440
    and memtable_throughput = 128;

 nodetool -h dsdb4 tpstats
Pool Name                    Active   Pending      Completed
ReadStage                        32       281         456598
RequestResponseStage              0         0         797237
MutationStage                     0         0         499205
ReadRepairStage                   0         0         149077
GossipStage                       0         0         217227
AntiEntropyStage                  0         0              0
MigrationStage                    0         0            201
MemtablePostFlusher               0         0           1842
StreamStage                       0         0              0
FlushWriter                       0         0           1841
FILEUTILS-DELETE-POOL             0         0           3670
MiscStage                         0         0              0
FlushSorter                       0         0              0
InternalResponseStage             0         0              0
HintedHandoff                     0         0             15

cfstats

Keyspace: StressKeyspace
        Read Count: 460988
        Read Latency: 38.07654727454945 ms.
        Write Count: 499205
        Write Latency: 0.007409593253272703 ms.
        Pending Tasks: 0
                Column Family: StressStandard
                SSTable count: 9
                Space used (live): 247408645485
                Space used (total): 247408645485
                Memtable Columns Count: 0
                Memtable Data Size: 0
                Memtable Switch Count: 1878
                Read Count: 460989
                Read Latency: 28.237 ms.
                Write Count: 499205
                Write Latency: NaN ms.
                Pending Tasks: 0
                Key cache capacity: 1000000
                Key cache size: 299862
                Key cache hit rate: 0.6031833150384193
                Row cache: disabled
                Compacted row minimum size: 219343
                Compacted row maximum size: 5839588
                Compacted row mean size: 497474


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