Question

i know, there is no transaction support on mongo DB. But now i need to read an value of an document, increment by 1 and write the new value.

Or – different way:
Update an element and read the value at the same time.
For this i like to use find and modify : http://www.mongodb.org/display/DOCS/findAndModify+Command

this command updates an document and returns the value before updating.
Is this happens in on (same like) transaction?
The point is: is it possible that an other session updates the same value between the two steps of the other session?

(sorry, for me it’s hard to explain – i hope you understand what i’m trying to say)

thank you.

Answer 1

findAndModify command is atomic. Which means that no other operation can happen between find and modify parts. This command was made exactly for things like incrementing counters/settings flags and reading them at the same time.