Tom Lane wrote:
"Florian G. Pflug" <[EMAIL PROTECTED]> writes:
I plan to submit a proposal for implementing support for
read-only queries during wal replay as a "Google Summer of Code 2007"
project.


You are discussing this on the wrong list.
So what list would be more appropriate?

B) Split StartupXLOG into two steps. The first (Recovery) will process
    only enough wal to bring the system into a consistent state,

How will you know what that is?
With the same logic that postgres uses now to bring an file-system backup
into a consistent state when doing PITR.

C) Combine A) and B), in the simplest possible way.
    Introduce a global R/W lock, which is taken by the Replay part
    of B) in write mode before replaying a chunk, then released,
    and immediatly reaquired before replaying the next chunk.

That seems certain to result in intolerable performance, for both the
queries and the replay process.

That depends entirely on the usecase. And besides, this limitation could
and probably would be adressed in the future. I think a step-by-step
approach is more likely to be successfull then attempting to solve
all problems at once.

greetings, Florian Pflug




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