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Gmane

From: Abhishek <abhishek.rhce-Re5JQEeQqe8AvxtiuMwx3w <at> public.gmane.org>
Subject: Finding Correct OpLogsize
Newsgroups: gmane.comp.db.mongodb.user
Date: Thursday 6th May 2010 10:46:15 UTC (over 8 years ago)
Hi,

Can anyone tell me how can i predict size of OpLog size My Database is
going to be really big +200G?

I have setup replication and following is replication information.


> db.printReplicationInfo();
configured oplog size:   12878.610432MB
log length start to end: 9938secs (2.76hrs)
oplog first event time:  Thu May 06 2010 13:17:43 GMT+0530 (IST)
oplog last event time:   Thu May 06 2010 16:03:21 GMT+0530 (IST)
now:                     Thu May 06 2010 16:03:27 GMT+0530 (IST)

In documentation i did not understand how they figured out adding data
rate in database. Like following doc is saying 524MB/hr. Please tell
me how can i calculate this.




< mongod documentation >

Figuring out the OpLog size

If the current oplog size is wrong, how do you figure out what's
right? The goal is not to let the oplog age out in the time it takes
to clone the database. The first step is to print the replication
info. On the master node, run this command:

> db.printReplicationInfo();

You'll see output like this:

configured oplog size:   1048.576MB
log length start to end: 7200secs (2hrs)
oplog first event time:  Wed Mar 03 2010 16:20:39 GMT-0500 (EST)
oplog last event time:   Wed Mar 03 2010 18:20:39 GMT-0500 (EST)
now:                     Wed Mar 03 2010 18:40:34 GMT-0500 (EST)

This indicates that you're adding data to the database at a rate of
524MB/hr. If an initial clone takes 10 hours, then the oplog should be
at least 5240MB, so something closer to 8GB would make for a safe
bet.

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