oplog file size increase over the oplogSizeMB setting.

[Kanako Nakai]

I set 15GB to oplogSizeMB in mongod.conf and loaded 100GB data using ycsb. 

After data load, I checked oplog size increased 19GB.

I complete thought oplog size can not increase over the 15GB, but I got diffrent result.

Does anyone know reason why oplog size increase over the oplogSizeMB setting or Is this a bug?

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mongod.conf

replication:

   oplogSizeMB: 15360  <--

   replSetName: Rpl01

   secondaryIndexPrefetch: all

   enableMajorityReadConcern: false

Rpl01:PRIMARY> rs.printReplicationInfo()

configured oplog size:   15360MB  <--

log length start to end: 65292secs (18.14hrs)

oplog first event time:  Mon Oct 30 2017 15:24:25 GMT+0900 (JST)

oplog last event time:   Tue Oct 31 2017 09:32:37 GMT+0900 (JST)

now:                     Tue Oct 31 2017 09:32:44 GMT+0900 (JST)

Rpl01:PRIMARY> db.getCollectionNames().forEach(function(n){print(n + "," + db[n].stats().storageSize/1024/1024/1024 + "GByte")})

me,0.0000152587890625GByte

oplog.rs,18.406475067138672GByte  <--

replset.election,0.000034332275390625GByte

replset.minvalid,0.000034332275390625GByte

startup_log,0.000034332275390625GByte

system.replset,0.000030517578125GByte

$ ls -la ./data/local

total 19G

drwxr-xr-x 2 mongodb mongodb 4.0K Oct 28 14:05 .

drwxr-xr-x 7 mongodb mongodb  276 Oct 31 09:25 ..

-rw-r--r-- 1 mongodb mongodb  36K Oct 30 18:40 collection-0--2786113240891747328.wt

-rw-r--r-- 1 mongodb mongodb  19G Oct 31 09:25 collection-12--2786113240891747328.wt  <--

-rw-r--r-- 1 mongodb mongodb  36K Oct 30 18:40 collection-20--2786113240891747328.wt

-rw-r--r-- 1 mongodb mongodb  16K Oct 30 18:39 collection-2--2786113240891747328.wt

-rw-r--r-- 1 mongodb mongodb  32K Oct 30 18:39 collection-4--2786113240891747328.wt

-rw-r--r-- 1 mongodb mongodb  36K Oct 30 18:40 collection-6--2786113240891747328.wt

-rw-r--r-- 1 mongodb mongodb  36K Oct 30 18:40 index-1--2786113240891747328.wt

-rw-r--r-- 1 mongodb mongodb  16K Oct 28 14:05 index-21--2786113240891747328.wt

-rw-r--r-- 1 mongodb mongodb  16K Oct 28 14:01 index-3--2786113240891747328.wt

-rw-r--r-- 1 mongodb mongodb  16K Oct 28 14:01 index-5--2786113240891747328.wt

-rw-r--r-- 1 mongodb mongodb  16K Oct 28 14:01 index-7--2786113240891747328.wt

[Kevin Adistambha]

Hi

What is your MongoDB version? There was a similar issue that was fixed in MongoDB 3.0.8 (see SERVER-21553)

If your MongoDB version is newer than 3.0.8, do you observe further growth of the oplog as more documents are inserted, or is there an upper limit to the file size?

Best regards
Kevin

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