hsnusonic commented on a change in pull request #996:
URL: https://github.com/apache/orc/pull/996#discussion_r781699986
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File path: java/core/src/java/org/apache/orc/impl/RecordReaderUtils.java
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@@ -182,10 +182,13 @@ public static long estimateRgEndOffset(boolean
isCompressed,
long streamLength) {
// 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.
+ // 512 is the MAX_SCOPE defined in RunLengthIntegerWriterV2.
+ // 8 is the maximum size of bytes for each value (see
RunLengthIntegerWriterV2.zzBits100p).
+ // We need to calculate the maximum number of blocks by bufferSize
accordingly.
+ int stretchFactor = bufferSize > 0 ? 2 + (512 * 8 - 1) / bufferSize : 2;
Review comment:
We are actually doing a round-up operation for `(512 * 8) / bufferSize`.
We can interpret the formula as `1 (for uncompressed bytes in buffer) +
Math.ceil(512 * 8 / (float) bufferSize)`. The second part can be expanded to `1
+ (512 * 8 - 1) / bufferSize`. I just thought that we can avoid floating point
calculation here.
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