Foreground write

Whenever an sqlexec thread writes a buffer to disk, it is termed a foreground write. A foreground write occurs when an sqlexec thread searches through the LRU queues on behalf of a user but cannot locate an empty or unmodified buffer.

To make space, the sqlexec thread flushes pages, one at a time, to hold the data to be read from disk. For more information, see FIFO/LRU queues.

If the sqlexec thread must perform buffer flushing just to acquire a shared-memory buffer, performance can suffer. Foreground writes must be avoided. To display a count of the number of foreground writes, run onstat -F. If you find that foreground writes are occurring on a regular basis, tune the value of the page-cleaning parameters. Either increase the number of page cleaners or decrease the BUFFERPOOL lru_max_dirty value.

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