set b-tree as default #540
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keegancsmith
approved these changes
Feb 20, 2023
| @@ -1775,7 +1775,7 @@ func TestListRepos(t *testing.T) { | |||
| Stats: RepoStats{ | |||
| Shards: 1, | |||
| Documents: 4, | |||
| IndexBytes: 300, | |||
| IndexBytes: 412, | |||
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combinedNgramOffset.SizeBytes() didn't account for header bytes (slice headers mostly), has a compressed representation for ascii, and has a lower overhead for low ngram counts (like here in the test case). An empty btreeIndex already uses 92 bytes. However, the cost amortizes once the tree fills up. Even small repos have a fulll b-tree with ~1000 leaf nodes.
stefanhengl
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Mar 14, 2023
I removed the code for binary search ngrams in #540, so this check is not needed anymore.
stefanhengl
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Mar 14, 2023
I removed the code for binary search ngrams in #540, so this check is not needed anymore.
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The use of a b-tree has proven to be successful. Webserver's heap for a production instance of Sourcegraph shrank by 45% without a noticable impact on latency. Hence we set the b-tree as default. It can be disabled by setting
ZOEKT_DISABLE_BTREE=truefor webserver.At the same time we remove
binarySearchNgram, because it uses more disk accesses than the b-tree and keeps a reference to the posting offsets.Once the b-tree has proven itself over a longer period of time, I will remove the alternative code path (
combinedNgramOffset) and clean up the temporary structs and interfaces I created.Test plan: