I am using mongo shard distribution system. This system performs slow as the data size increases. I checked with profiler and saw split vector is taking to much time while running.

It happened after a day when one of my shard replica set went down and i had to remove that from cluster. Now i am running a single shard replica cluster. I have disabled the balancer as currently there is no second shard. Could you please help me to under stand why this process is slow.

1 Answer 1


The splitVector commands are slow because your system is slow, it's not the cause of the slowness itself - it just happens to be running frequently and hence is showing up a lot in your logs - it is a symptom not a cause (unless you are running many, many mongos processes and hitting an edge case). People often make the same mistake by misdiagnosing slow serverStatus commands (run every 60 seconds by MMS monitoring) as a root cause.

Usually the slowness is because your system is oversubscribed and hitting a bottleneck somewhere, but you have not provided enough information to make a guess as to what your issue is. I would recommend looking for other evidence in the logs as well as the usual suspects (IO, CPU, Memory) to narrow down the actual root cause here.

  • Hi Adam I am running a mongo shard set up which has three mongos servers one is used for writing data one is used for reading data and one is used for running some aggergation scripts. I have one mongo shard which is system with 560 Ram currently i am having 1.6 TB data on this system. My question is can i put another shard in thsi system with this much data already in the system. Second my system become unresponsive for writes between 2 pm to 6 PM and if i run mongostat there are no faults. But it does not respond to the apache servers writing data in system between these hours only.
    – viren
    Commented May 27, 2014 at 9:27

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