Conversation
A merge reads stored fields front to back while searches read the same file at random, and getMergeInstance() cloned the mapping the reader already held, so the advice a merge got came down to who opened the segment first. Read advice covers a whole mapping, so the merge instance opens the data file for itself with SEQUENTIAL rather than re-advising the mapping searches are on. The original reader owns that mapping and closes it, since merge instances are never closed.
jimczi
force-pushed
the
agent/stored-fields-merge-advice
branch
from
September 18, 2026 09:19
d33ec5c to
3919cbd
Compare
github-actions
Bot
added
module:core/index
module:core/codecs
module:test-framework
labels
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
1 participant
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
A merge reads stored fields front to back, while searches read the same file at random.
getMergeInstance()clones the mapping the reader already holds, so whether a merge gets sequentialreads comes down to who opened the segment first. Asking for them in place is not an option, since
read advice applies to a whole mapping and searches are on it.
So a merge opens the data file for itself with
DataAccessHint.SEQUENTIAL, and searches keep themapping they have. The original reader owns that second mapping and closes it, since merge instances
are never closed.