Native Transport Requests in Cassandra - cassandra

Question

I got some points about Native Transport Requests in Cassandra using this link : What are native transport requests in Cassandra?
As per my understanding, any query I execute in Cassandra is an Native Transport Requests.
I frequently get Request Timed Out error in Cassandra and I observed the following logs in Cassandra debug log and as well as using nodetool tpstats
/var/log/cassandra# nodetool tpstats
Pool Name Active Pending Completed Blocked All time blocked
MutationStage 0 0 186933949 0 0
ViewMutationStage 0 0 0 0 0
ReadStage 0 0 781880580 0 0
RequestResponseStage 0 0 5783147 0 0
ReadRepairStage 0 0 0 0 0
CounterMutationStage 0 0 14430168 0 0
MiscStage 0 0 0 0 0
CompactionExecutor 0 0 366708 0 0
MemtableReclaimMemory 0 0 788 0 0
PendingRangeCalculator 0 0 1 0 0
GossipStage 0 0 0 0 0
SecondaryIndexManagement 0 0 0 0 0
HintsDispatcher 0 0 0 0 0
MigrationStage 0 0 0 0 0
MemtablePostFlush 0 0 799 0 0
ValidationExecutor 0 0 0 0 0
Sampler 0 0 0 0 0
MemtableFlushWriter 0 0 788 0 0
InternalResponseStage 0 0 0 0 0
AntiEntropyStage 0 0 0 0 0
CacheCleanupExecutor 0 0 0 0 0
Native-Transport-Requests 0 0 477629331 0 1063468
Message type Dropped
READ 0
RANGE_SLICE 0
_TRACE 0
HINT 0
MUTATION 0
COUNTER_MUTATION 0
BATCH_STORE 0
BATCH_REMOVE 0
REQUEST_RESPONSE 0
PAGED_RANGE 0
READ_REPAIR 0
1) What is the All time blocked state?
2) What is this value : 1063468 denotes? How harmful it is?
3) How to tune this?

Answer 1

Each request is taken processed by the NTR stage before being handed off to read/mutation stage but it still blocks while waiting for completion. To prevent being overloaded the stage starts to block tasks being added to its queue to apply back pressure to client. Every time a request is blocked the all time blocked counter is incremented. So 1063468 requests have at one time been blocked for some period of time due to having to many requests backed up.
In situations where the app has spikes of queries this blocking is unnecessary and can cause issues so you can increase this queue limit with something like -Dcassandra.max_queued_native_transport_requests=4096 (default 128). You can also throttle requests on client side but id try increasing queue size first.
There also may be some request thats exceptionally slow that is clogging up your system. If you have monitoring setup, look at high percentile read/write coordinator latencies. You can also use nodetool proxyhistograms. There may be something in your data model or queries that is causing issues.