Pending tasks are not a queue, they are an estimation of the amount of work it would take to reach a perfect compaction point, but the compactions aren’t independent from one another.  For instance, with LCS you may have a compaction from L0 -> L1, which triggers a L1 -> L2 compaction.  You can’t do them in parallel because one depends on the other.

On Sep 21, 2017, at 3:10 PM, ZAIDI, ASAD A <az192g@att.com> wrote:

Hello Folks,
 
Is it possible to findout detail of those 275 pending tasks compactionstats command output is showing? 
I’ve bumpedup concurrent_compactors to 25 though not all threads are compacting, only 8 threads are being used so i’m wondering how can I utilize all configured concurrent compactors when there are still pending tasks?
 
 
 
[cassandra@server]$ nodetool compactionstats -H
pending tasks: 275
                                     id   compaction type     keyspace                            table   completed       total    unit   progress
   64c55e50-9f17-11e7-94ce-0fe8b18d4e6c        Compaction   corporate          usrcnt_location_by_hour    70.47 MB   178.29 MB   bytes     39.52%
   65930e90-9f17-11e7-94ce-0fe8b18d4e6c        Compaction   corporate                  visi_det_rollup    87.46 MB   208.54 MB   bytes     41.94%
   73c34250-9f17-11e7-94ce-0fe8b18d4e6c        Compaction   corporate                  visi_det_rollup      3.1 MB   122.41 MB   bytes      2.53%
   d4e2cde0-9f16-11e7-94ce-0fe8b18d4e6c        Compaction   corporate                timing_by_account     1.64 GB     5.96 GB   bytes     27.59%
   6a430210-9f17-11e7-94ce-0fe8b18d4e6c        Compaction   corporate                  stream_host_etl   127.05 MB   162.78 MB   bytes     78.05%
   6c997530-9f17-11e7-94ce-0fe8b18d4e6c        Compaction   corporate                       det_rollup    40.44 MB   131.33 MB   bytes     30.79%
   59fc4a60-9f17-11e7-94ce-0fe8b18d4e6c        Compaction   corporate                       det_rollup   180.48 MB   250.69 MB   bytes     72.00%
   607739e0-9f17-11e7-94ce-0fe8b18d4e6c        Compaction   corporate                       det_rollup   131.36 MB   256.18 MB   bytes     51.28%
   659817a0-9f17-11e7-94ce-0fe8b18d4e6c        Compaction   corporate                     station_data      108 MB   267.68 MB   bytes     40.35%
Active compaction remaining time :        n/a
 
==============
 
[cassandra@server]$ nodetool tpstats
 
Pool Name                    Active   Pending      Completed   Blocked  All time blocked
MutationStage                     1         0      200764219         0                 0
ReadStage                         0         0              0         0                 0
RequestResponseStage              0         0             37         0                 0
ReadRepairStage                   0         0              0         0                 0
CounterMutationStage              0         0              0         0                 0
HintedHandoff                     0         0             16         0                 0
MiscStage                         0         0              0         0                 0
CompactionExecutor                8         8          19129         0                 0
MemtableReclaimMemory             0         0          14586         0                 0
PendingRangeCalculator            0         0              6         0                 0
GossipStage                       0         0          75457         0                 0
MigrationStage                    0         0           2558         0                 0
MemtablePostFlush                 1         1          15908         0                 0
ValidationExecutor                0         0              0         0                 0
Sampler                           0         0              0         0                 0
MemtableFlushWriter               1         1          14573         0                 0
InternalResponseStage             0         0              0         0                 0
AntiEntropyStage                  0         0              0         0                 0
CacheCleanupExecutor              0         0              0         0                 0
 
Message type           Dropped
READ                         0
RANGE_SLICE                  0
_TRACE                       0
MUTATION                     0
COUNTER_MUTATION             0
REQUEST_RESPONSE             0
PAGED_RANGE                  0
READ_REPAIR                  0
 
 
 
Thanks/Asad