shuwenwei opened a new pull request, #18394:
URL: https://github.com/apache/iotdb/pull/18394
## Description
For wide aligned devices, a query that only touches a few columns currently
clones the entire aligned TVList (all columns) in the working memtable, which
is very expensive in both memory and time. This PR makes the query-side clone
copy only the accessed columns and move the remaining uncloned columns by
reference into the clone, so partial-column queries no longer duplicate the
whole aligned device.
### Changes
- `AlignedTVList`: add `clone(Set<Integer>)`, `cloneColumnDataTo` and
`moveUnclonedColumnsTo` so the clone keeps only the accessed columns and
the
uncloned columns are transferred by reference into the new working list.
- `ResourceByPathUtils.prepareTvListMapForQuery`: pass the accessed column
index list into the clone path; re-fetch and re-verify the working TVList
under the memChunk lock after acquiring its `queryListLock`, and perform
clone + column move + working-list swap in the same memChunk critical
section so a concurrent query never observes a detached list whose columns
were already moved away.
- `FragmentInstanceContext`: track column-level access for AlignedTVList.
### Tests
- `AlignedTVListTest`: partial clone keeps only the accessed columns and
moves
the uncloned ones by reference.
- `FragmentInstanceExecutionTest`: querying partial columns of an aligned
device returns correct results.
<hr>
This PR has:
- [x] been self-reviewed.
- [ ] concurrent read
- [ ] concurrent write
- [x] concurrent read and write
- [ ] added documentation for new or modified features or behaviors.
- [ ] added Javadocs for most classes and all non-trivial methods.
- [ ] added or updated version, license, or notice information
- [x] added comments explaining the "why" and the intent of the code
wherever would not be obvious
- [x] added unit tests or modified existing tests to cover new code paths
- [ ] added integration tests.
- [ ] been tested in a test IoTDB cluster.
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