[Dump-devel] Multiple slaves stepping on each other

[Phillip S. <ps...@cf...>]

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Dump throughput seems to suffer significantly because each of the 3
slaves are simultaneously trying to read from the disk, causing
unnecessary seeking.  I'm a little unsure of how to fix the problem
though.  Right now, each slave reads the data blocks, then optionally
compresses, then waits for the signal from the previous slave to write
it to the output.  Instead, I think it needs to be signaled when it is
time to start reading, do the reading, signal the next slave to read,
optionally do the compression, then wait to be signaled to do the
writing.  That way multiple slaves can be compressing at the same time,
but only one can be reading or writing at a time.

Right now it uses SIGUSR2 to notify the next slave to proceed, but two
signals can not be queued at the same time.  Should it also use SIGUSR1
for the other signal, or is there a better way than signals to notify
the next slave to proceed?
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