mongo best practice/data skew

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Gary Leong

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Aug 8, 2014, 5:18:15 PM8/8/14
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i already posted this on stack overflow, but i figure i ping this google group too. 

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we're having some problems with mongodb. it was great the first year, but the last 2 or 3 years we have noticed:

1) skewed data/cluster inconsistency

e.g.

master yields count of 83, slave1 yields count of 73, slave2 yields count of 0

  • this has happened 3 times already. we fix it by blowing out the slaves and starting replication from scratch. it solves the problems. is this a known issue with mongo or is it just our application that interacts with it funny?

2) according to new relic and munin

last friday, our primary node shows high i/o latency. new relics shows it is indexing 98% of the time. the cluster grinds to being unusable.

i had to shutdown the master and have the cluster promote a slave to master. it solved the problem. when the former master is put back online, it shows that it is in recovery mode. really weird.

i suppose i want to at best have a solution and at minimally, see if this is common.

thanks in advance!


Asya Kamsky

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Aug 10, 2014, 10:43:26 AM8/10/14
to mongodb-user

You haven't provided enough information to know whether this problem is in MongoDB or in your application or in the way you are using/checking what's going on.

Can you start by telling us your MongoDB version, your replica set topology, what your client is using to interact with it (driver, version) how you checked this data "inconsistency", etc.

Asya

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