pgaref commented on a change in pull request #996:
URL: https://github.com/apache/orc/pull/996#discussion_r783916769
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File path: java/core/src/java/org/apache/orc/impl/RecordReaderUtils.java
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@@ -180,12 +180,18 @@ public static long estimateRgEndOffset(boolean
isCompressed,
boolean isLast,
long nextGroupOffset,
long streamLength) {
+ if (isCompressed && bufferSize <= 0) {
+ throw new IllegalArgumentException("BufferSize must be > 0 but was " +
bufferSize);
+ }
// figure out the worst case last location
// if adjacent groups have the same compressed block offset then stretch
the slop
- // by factor of 2 to safely accommodate the next compression block.
- // One for the current compression block and another for the next
compression block.
+ // by a factor to safely accommodate the next compression block.
+ // We need to calculate the maximum number of blocks by bufferSize
accordingly.
+ final int stretchFactor = isCompressed
+ ? 2 + (MAX_VALUES_LENGTH * MAX_BIT_WIDTH / 8 - 1) / bufferSize
Review comment:
I am not sure I understand the formula here -- first of all we divide by
8 is the conversion from bits to Bytes?
I thought this is a round up operation?
I would also structure this a bit differently:
`// figure out the worst case last location
long slop = WORST_UNCOMPRESSED_SLOP;
// if adjacent groups have the same compressed block offset then stretch
the slop
// by a factor to safely accommodate the next compression block.
// We need to calculate the maximum number of blocks by bufferSize
accordingly.
if (isCompressed) {
final int stretchFactor = 2 + (MAX_VALUES_LENGTH * MAX_BIT_WIDTH / 8 -
1) / bufferSize;
slop = stretchFactor * (OutStream.HEADER_SIZE + bufferSize);
}`
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