sgup432 commented on PR #16358:
URL: https://github.com/apache/lucene/pull/16358#issuecomment-4890056944
Example of how the data layout on the disk changes after this PR:
**Before (fixed schema, version ≤ 2):**
```
Per entry:
[1B: numLevels]
per level (high → low):
[4B: maxDocID] [4B: minDocID] [8B: maxValue] [8B: minValue] [4B:
docCount]
= exactly 28 bytes, always
Single-level entry = 1 + 28 = 29 bytes
Two-level entry = 1 + 56 = 57 bytes
Reader skips by precomputed offset:
skipBytes(SKIP_INDEX_JUMP_LENGTH_PER_LEVEL[level])
```
---
**After (stats-based, version 3):**
```
Per entry:
[1B: numLevels]
[4B: intervalLength]
per level (high → low):
[4B: maxDocID]
[4B: entryLength]
[1B: SKIP_STAT_RANGE (0x01)]
[4B: minDocID] [8B: maxValue] [8B: minValue] [4B: docCount]
Single-level entry = 1 + 4 + (4 + 4 + 1 + 24) = 38 bytes
Two-level entry = 1 + 4 + 2×(4 + 4 + 1 + 24) = 71 bytes
Reader skips by stored length: seek(intervalEnd)
```
---
**After, with a future stat (sum) added:**
```
Per entry:
[1B: numLevels]
[4B: intervalLength]
per level (high → low):
[4B: maxDocID]
[4B: entryLength]
[1B: SKIP_STAT_RANGE (0x01)]
[4B: minDocID] [8B: maxValue] [8B: minValue] [4B: docCount]
[1B: SKIP_STAT_SUM (0x02)] ← just appended
[8B: sumValue] ← no other changes needed
```
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