Scott Carey wrote:
This is because an fsync on ext3 flushes _all dirty pages in the file system_ to disk, not just those for the file being fsync'd.
One partition for WAL, one for data. If using ext3 this is essentially a performance requirement no matter how your array is set up underneath.
Unless you want the opposite of course. Some systems split out the WAL
onto a second disk, only to discover checkpoint I/O spikes become a
problem all of the sudden after that. The fsync calls for the WAL
writes keep the write cache for the data writes from ever getting too
big. This slows things down on average, but makes the worst case less
stressful. Free lunches are so hard to find nowadays...
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Greg Smith 2ndQuadrant US Baltimore, MD
PostgreSQL Training, Services and Support
greg@xxxxxxxxxxxxxxx www.2ndQuadrant.us
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