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Answer 1

+1 A:

Is this relevant?

durability: added occasinal file sync
default: sync every 60 seconds, confiruable with syncdelay

http://github.com/mongodb/mongo/commit/c44bff08fd95616302a73e92b48b2853c1fd948d

Noah Watkins 2010-09-17 15:16:03

Answer 2

+1 A:

Niels van der Rest 2010-09-17 16:21:59

Ok, so the database data has satisfied D in ACID every 60 seconds cause fsync() is executed every minute saving all the data in memory to disk right?

never_had_a_name 2010-09-17 16:30:17

@ajsie: Technically not. To satisfy D, the data has to be written to disk **when the database responds successfully**. But MongoDB has written the data only to memory at that point, so the data is not 'durable' yet. It *is* durable after at most 60 seconds, due to the fsync().

Niels van der Rest 2010-09-17 17:04:46

@Niels van der Rest: Is MongoDB just violating the D in ACID or are there other violations as well?

never_had_a_name 2010-09-18 02:58:05

@ajsie: See my updated answer.

Niels van der Rest 2010-09-18 10:15:23

@Niels: But if I have to make a transaction that spans over 2 documents (eg. transferring money) then I guess its not reliable to use MongoDB for that. You say that MongoDB violates all the ACID properties. Do you know which ones CouchDB violates?

never_had_a_name 2010-09-18 21:49:41

@ajsie: I'm not very familiar with CouchDB, but I believe it has better ACID support than MongoDB. Probably good material for a new question :)

Niels van der Rest 2010-09-18 22:16:54

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Why doesn't MongoDB use fsync()?

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