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Bryan Boreham 793a689d1f Iterators: re-implement mergeEntryIterator using loser.Tree for performance (#8637) ... **What this PR does / why we need it**: Building on #8351, this re-implements `mergeEntryIterator` using `loser.Tree`; the benchmark says it goes much faster but uses a bit more memory (while building the tree). ``` name old time/op new time/op delta SortIterator/merge_sort-4 10.7ms ± 4% 2.9ms ± 2% -72.74% (p=0.008 n=5+5) name old alloc/op new alloc/op delta SortIterator/merge_sort-4 11.2kB ± 0% 21.7kB ± 0% +93.45% (p=0.008 n=5+5) name old allocs/op new allocs/op delta SortIterator/merge_sort-4 6.00 ± 0% 7.00 ± 0% +16.67% (p=0.008 n=5+5) ``` The implementation is very different: rather than relying on iterators supporting `Peek()`, `mergeEntryIterator` now pulls items into its buffer until it finds one with a different timestamp or stream, and always works off what is in the buffer. The comment `"[we] pop the ones whose common value occurs most often."` did not appear to match the previous implementation, and no attempt was made to match this comment. A `Push()` function was added to `loser.Tree` to support live-streaming. This works by finding or making an empty slot, then re-running the initialize function to find the new winner. A consequence is that the previous "winner" value is lost after calling `Push()`, and users must call `Next()` to see the next item. A couple of tests had to be amended to avoid assuming particular behaviour of the implementation; I recommend that reviewers consider these closely. **Checklist** - [x] Reviewed the [`CONTRIBUTING.md`](https://github.com/grafana/loki/blob/main/CONTRIBUTING.md) guide (**required**) - NA Documentation added - [x] Tests updated - NA `CHANGELOG.md` updated - NA Changes that require user attention or interaction to upgrade are documented in `docs/sources/upgrading/_index.md`		2 years ago
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tree.go	Iterators: re-implement mergeEntryIterator using loser.Tree for performance (#8637)	2 years ago
tree_test.go	Iterators: re-implement mergeEntryIterator using loser.Tree for performance (#8637)	2 years ago