index: fix repeated v2 index merge panic#101
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Repeated merges of v2 indexes could treat the on-disk posting-list sentinel, invalidTrigram (0x00ffffff), as a normal trigram because the merge reader used ^uint32(0) as its internal EOF marker. That let duplicate serialized sentinels accumulate in the posting index, and a later cindex run could panic with no progress while merging. Use invalidTrigram consistently in postMapReader and merge sentinel handling. Restore lazy posting-list writes so ordinary trigrams with no surviving file IDs are omitted while the final sentinel is still emitted. Add a repeated-merge regression test that checks merged v2 indexes stay valid and do not grow extra posting entries. Fixes google#100.
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Fixes #100.
Repeated cindex runs against a v2 index could panic during merge with:
The merge reader used ^uint32(0) as its internal EOF marker, while the on-disk posting-list sentinel is invalidTrigram (0x00ffffff). As a result, merge treated the serialized sentinel as a normal trigram and then emitted another sentinel at EOF. Each successful merge accumulated another serialized sentinel and a later merge could stop making progress through the duplicate sentinel entries.
This change makes merge sentinel handling use invalidTrigram consistently. It also restores lazy posting-list writes so ordinary trigrams with no surviving file IDs are omitted, while the final sentinel is still emitted.
A regression test now repeatedly merges v2 indexes and checks that the merged index remains valid and does not grow extra posting entries.
Testing:
go test ./...I also verified the issue reproduction manually on linux/amd64 with repeated no-argument cindex runs. The patched binary completed repeated reindexes, cindex-check -list passed and the final posting index contained exactly one 0xffffff sentinel with no non-increasing trigram entries.