Copilot commented on code in PR #7835:
URL: https://github.com/apache/hadoop/pull/7835#discussion_r2253585143
##########
hadoop-tools/hadoop-azure/src/main/java/org/apache/hadoop/fs/azurebfs/services/AbfsInputStream.java:
##########
@@ -511,8 +512,12 @@ private int readInternal(final long position, final byte[]
b, final int offset,
}
int receivedBytes;
- // queue read-aheads
- int numReadAheads = this.readAheadQueueDepth;
+ /*
+ * Number of prefetches to queue for each request is configurable.
+ * For the first read of this input stream, we don't read ahead but keep
+ * the current read data in cache as pattern might not be sequential.
+ */
+ int numReadAheads = firstRead? 1 : this.readAheadQueueDepth;
Review Comment:
[nitpick] The ternary operator lacks spaces around the `?` operator, which
deviates from Java coding conventions. It should be `firstRead ? 1 :
this.readAheadQueueDepth`.
```suggestion
int numReadAheads = firstRead ? 1 : this.readAheadQueueDepth;
```
##########
hadoop-tools/hadoop-azure/src/main/java/org/apache/hadoop/fs/azurebfs/services/AbfsInputStream.java:
##########
@@ -348,14 +348,15 @@ private int readOneBlock(final byte[] b, final int off,
final int len) throws IO
if (alwaysReadBufferSize) {
bytesRead = readInternal(fCursor, buffer, 0, bufferSize, false);
} else {
- // Enable readAhead when reading sequentially
+ // Switch between enabling and disabling read ahead based on the
workload read pattern.
if (-1 == fCursorAfterLastRead || fCursorAfterLastRead == fCursor ||
b.length >= bufferSize) {
- LOG.debug("Sequential read with read ahead size of {}", bufferSize);
+ // Sequential read pattern detected. Enable read ahead.
+ LOG.debug("Sequential read with read size of {} and read ahead
enabled", bufferSize);
bytesRead = readInternal(fCursor, buffer, 0, bufferSize, false);
} else {
- // Enabling read ahead for random reads as well to reduce number of
remote calls.
+ // Random read pattern detected. Disable read ahead.
int lengthWithReadAhead = Math.min(b.length + readAheadRange,
bufferSize);
- LOG.debug("Random read with read ahead size of {}",
lengthWithReadAhead);
+ LOG.debug("Random read with read size of {} and read ahead
disabled", lengthWithReadAhead);
Review Comment:
The log message mentions 'read ahead disabled' but the variable logged is
`lengthWithReadAhead`, which suggests read-ahead is still being used. This is
confusing and inconsistent with the message.
```suggestion
LOG.debug("Random read with requested size {} (read ahead range:
{}), actual read size: {}, read ahead disabled", b.length, readAheadRange,
lengthWithReadAhead);
```
##########
hadoop-tools/hadoop-azure/src/main/java/org/apache/hadoop/fs/azurebfs/services/AbfsInputStream.java:
##########
@@ -348,14 +348,15 @@ private int readOneBlock(final byte[] b, final int off,
final int len) throws IO
if (alwaysReadBufferSize) {
bytesRead = readInternal(fCursor, buffer, 0, bufferSize, false);
} else {
- // Enable readAhead when reading sequentially
+ // Switch between enabling and disabling read ahead based on the
workload read pattern.
if (-1 == fCursorAfterLastRead || fCursorAfterLastRead == fCursor ||
b.length >= bufferSize) {
- LOG.debug("Sequential read with read ahead size of {}", bufferSize);
+ // Sequential read pattern detected. Enable read ahead.
+ LOG.debug("Sequential read with read size of {} and read ahead
enabled", bufferSize);
Review Comment:
The log message mentions 'read size of {}' but logs `bufferSize` instead of
the actual read size (`b.length`). This could be misleading when debugging read
operations.
```suggestion
LOG.debug("Sequential read with read size of {} and read ahead
enabled", b.length);
```
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