The fun thing about oplogs is that they're only useful if you have the debug level turned way up, but if you do that on a moderately busy system, you run out of disk space in a couple of minutes.
I don't believe that's true. The oplog is what powers replication, so it must record every operation altering your data.
It's stored in a capped collection, so it stays the same size on disk. If you limit your oplog to only 100MB and have a busy system, you may only store 1 minute worth of operations, but disk size won't be affected.
Though, with 100MB your ability to have a useful oplog may be affected and your replica set will likely be unable to replicate fast enough to keep secondaries in-sync.
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[ 3.3 ms ] story [ 20.3 ms ] threadIt's stored in a capped collection, so it stays the same size on disk. If you limit your oplog to only 100MB and have a busy system, you may only store 1 minute worth of operations, but disk size won't be affected.
Though, with 100MB your ability to have a useful oplog may be affected and your replica set will likely be unable to replicate fast enough to keep secondaries in-sync.