Re: ACIDity of Prevayler 2.6

Arnaud -- You've got things a bit backwards. Yes, larger latencies are
acceptable for transactions than for queries, but that's exactly how
Prevayler behaves: Queries execute and return immediately whereas
transactions have to wait for writing to disk before executing and
returning. If transactions were written to disk after executing, then both
queries and transactions would execute immediately but both would wait for
writing to disk before returning. Throughput would be similar, but query
latency would be worse than it is now.

Transactions are already serialized concurrently (in memory) without
holding any locks, so don't worry about that. And the journal is written as
a continuous stream, not individual files, so moving/renaming is not an
option (and would be significantly slower).


On Fri, Nov 16, 2012 at 2:06 AM, Arnaud Masson <[email protected]> wrote:

> Many systems have much more queries than transactions,
> so transaction latency wouldn't be so critical.
>
> Moreover a transaction could be physically pre-serialized (or maybe in
> parallel thread) on the disk, in some temporary location, before the
> lock scope.
> After tx successful execution, just a quick "file move/rename" operation
> would be required to commit it to the journal, not a full serialization.

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