snvijaya commented on a change in pull request #2307:
URL: https://github.com/apache/hadoop/pull/2307#discussion_r489461371
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File path:
hadoop-tools/hadoop-azure/src/main/java/org/apache/hadoop/fs/azurebfs/services/AbfsInputStream.java
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@@ -180,9 +205,13 @@ private int readOneBlock(final byte[] b, final int off,
final int len) throws IO
// Enable readAhead when reading sequentially
if (-1 == fCursorAfterLastRead || fCursorAfterLastRead == fCursor ||
b.length >= bufferSize) {
+ LOG.debug("Sequential read with read ahead size of {}", bufferSize);
bytesRead = readInternal(fCursor, buffer, 0, bufferSize, false);
} else {
- bytesRead = readInternal(fCursor, buffer, 0, b.length, true);
+ // Enabling read ahead for random reads as well to reduce number of
remote calls.
+ int lengthWithReadAhead = Math.min(b.length + readAheadRange,
bufferSize);
+ LOG.debug("Random read with read ahead size of {}",
lengthWithReadAhead);
+ bytesRead = readInternal(fCursor, buffer, 0, lengthWithReadAhead,
true);
Review comment:
As with Parquet and ORC we have seen read patterns move from sequential
to random and vice versa. That being the case would it not be better to read
ahead to bufferSize always ? Providing options to read to lower bytes like 64
KB can actually lead to more IOPs. From our meeting yesterday too , one thing
we all agree to was lower the IOPs better and also better to read more than
smaller size.
So let remove the config for readAheadRange and instead always readAhead for
whats configured for bufferSize.
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