pymongo - Confirm basic understanding of MongoDB's acknowledged write concern -


using mongodb (via pymongo) in default "acknowledged" write concern mode, case if have line writes db (e.g. mapreduce outputs new collection) followed line reads db, read see changes write?

further, above true stricter write concerns "acknowledged," i.e. "journaled" , "replica acknowledged," not true in case of "unacknowledged"?

if write has been acknowledged, should have been written memory, subsequent query should current data. won't work if have replica set , allow reads secondaries.

journaled writes written journal file on disk, protects data in case of power / hardware failures, etc. shouldn't have impact on consistency, covered data in memory.

any replica configuration in write concern ensure writes need acknowledged majority / nodes in replica set. make difference if read replicas or protect data against unreachable / dead servers.


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