Details
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Improvement
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Status: Closed
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Critical
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Resolution: Fixed
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4.5.1, 4.6.3, 5.0.0
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Release Note
Description
When writing large amounts of data (e.g during compaction), read latency can be adversely affected if a single sync() is made at the end of writing all the data; as the IO subsystem has a large amount of outstanding writes to flush to disk. By issuing periodic sync() calls the affect on read latency can be signifcantly reduced.
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Image shows impact on bgwait of various different fsync thresholds. Tested on 4.5.1 toy build. Blue line denotes threshold change as do the markers on the graph at the correspond positions following levels: 0-1 == Off, 2-3 == 16M, 3-4 == 128K, 4-5 == 1M, >5 == 16M