fix(core): Account for size change on json object defragment #6053
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abhijat
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Nov 13, 2025
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Signed-off-by: Abhijat Malviya <[email protected]>
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![augmentcode[bot]](https://avatars.githubusercontent.com/in/1027498?s=60&v=4){kind=small}
| json_ptr = AllocateMR<JsonType>(DeepCopyJSON(old)); | ||
| DeleteMR<JsonType>(old); | ||
| if (const ssize_t delta = mr->used() - before; delta != 0) { | ||
| bytes_used += delta; |
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bytes_used is a size_t, while delta is ssize_t and may be negative; using += here can cause unsigned wraparound when defragmentation reduces size, leading to incorrect memory accounting.
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it is intentionally ssize_t, delta is expected to be negative. It should not lead to a wraparound though as delta is only caused by reallocation.
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For JSON type, after defragmentation used size may change. The change is recorded in page usage object, and the delta is propagated to the db stats object, so that metrics observe the change and reduction in memory usage (if any) correctly.
The delta update is in effect for all objects whose size changes, not just JSON type objects.