Database / Mnesia intermediate to advanced Interview questions
Why is batching multiple related writes into a single transaction usually better than many small transactions?
Every transaction carries fixed overhead beyond the actual work it does: acquiring locks, and for replicated tables, coordinating a two-phase commit round-trip with every replica. Running ten related writes as ten separate transactions pays that coordination overhead ten times over; wrapping them in one transaction pays it once, for all ten writes together.
%% worse: 10 separate round-trips of coordination overhead [mnesia:transaction(fun() -> mnesia:write(R) end) || R <- Records]. %% better: one transaction, one round-trip of overhead, for all writes mnesia:transaction(fun() -> [mnesia:write(R) || R <- Records] end).
Batching also means the writes are genuinely atomic together — if you actually need all ten to succeed or fail as a unit, separate transactions can't give you that guarantee at all, on top of the performance cost of the repeated coordination overhead.
What overhead does batching multiple writes into one transaction reduce?
What atomicity benefit does batching provide beyond raw performance?
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