read performance from synchronizing hfile.fddatainputstream
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Key: HBASE-2180
URL: https://issues.apache.org/jira/browse/HBASE-2180
Project: Hadoop HBase
Issue Type: Bug
Reporter: ryan rawson
Fix For: 0.21.0
deep in the HFile read path, there is this code:
synchronized (in) {
in.seek(pos);
ret = in.read(b, off, n);
}
this makes it so that only 1 read per file per thread is active. this prevents
the OS and hardware from being able to do IO scheduling by optimizing lots of
concurrent reads.
We need to either use a reentrant API (pread may be partially reentrant
according to Todd) or use multiple stream objects, 1 per scanner/thread.
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