MDEV-17613 Read sole now-partition for non-historical versioned query#5386
MDEV-17613 Read sole now-partition for non-historical versioned query#5386midenok wants to merge 5 commits into
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This pull request refactors partition pruning to use a local parts_bitmap within PART_PRUNE_PARAM instead of directly modifying part_info->read_partitions during the pruning process. At the end of pruning, the candidate partitions are narrowed by intersecting read_partitions with the newly computed parts_bitmap. A critical correctness issue was identified in sql/opt_range.cc where the return value retval is evaluated against the pre-pruned read_partitions bitmap rather than the post-intersection bitmap, which can lead to incorrect results. A code suggestion has been provided to update retval after the intersection.
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Pull request overview
Optimizes implicit (non-historical) queries on system-versioned tables whose history is stored in partitions by restricting reads to the current (“now”) partition, rather than relying on a row_end predicate, and adjusts partition pruning to respect an already-restricted candidate partition set.
Changes:
- Restrict
read_partitionsto the current versioning partition for implicit (noFOR SYSTEM_TIME) queries, and adjust guarding for repeated executions. - Refactor partition pruning to accumulate results in a separate bitmap and intersect with the incoming candidate
read_partitions(never widening it). - Add
partition_element::bitmap_range()helper and update related range computations; update versioning test expectation for EXPLAIN output.
Reviewed changes
Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.
Show a summary per file
| File | Description |
|---|---|
| sql/sql_select.cc | Restricts read_partitions to the “now” partition for implicit versioned queries. |
| sql/opt_range.cc | Makes pruning intersect-only by using a separate bitmap and intersecting with candidate partitions. |
| sql/partition_info.cc | Updates debug assertion to use bitmap_range() / total partitions helper. |
| sql/partition_element.h | Adds bitmap_range() helper to compute leaf-bitmap ranges for partitions/subpartitions. |
| sql/ha_partition.h | Uses bitmap_range() when summing records across a partition and its subpartitions. |
| mysql-test/suite/versioning/r/partition.result | Updates expected EXPLAIN Extra output (no longer “Using where” for implicit query). |
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Returns bit range for partition element.
prune_partitions() built the used-partition set directly in read_partitions: it cleared it, let find_used_partitions*() fill it, and in the index-merge case used it as scratch too - both buffer and result. The patch adds PART_PRUNE_PARAM::parts_bitmap and builds the return into it instead. read_partitions is produced from it only at the end: copied when the condition was analyzed (IMPOSSIBLE included, parts_bitmap left empty), or set to all locked partitions via mark_all_partitions_as_used() when nothing could be pruned. Pure refactoring: read_partitions ends up identical on every path. It decouples the pruning scratch from read_partitions, so a later commit can switch the final bitmap_copy() to bitmap_intersect() - letting pruning narrow a pre-set read_partitions (e.g. a versioned table selecting only its current partition) instead of overwriting it.
…ead of full rewrite read_partitions is reset from lock_partitions once per statement in open_table() (set_partition_bitmaps()), and prune_partitions() only intersects it with the pruned set instead of rebuilding it. mark_all_partitions_as_used() is dropped. Pure refactoring, results unchanged. It lets a restriction set on read_partitions before pruning survive it - needed when read_partitions is pre-restricted, e.g. a versioned table whose history is partitioned reads only the current partition.
When a versioned table stores its history in partitions, an implicit query (no FOR SYSTEM_TIME) needs only current rows, which all live in the current partition. Restrict read_partitions to that partition in vers_setup_conds() instead of relying on a row_end condition. read_partitions is reset to all partitions every statement in open_table(), so this restriction must be re-applied on each execution. Guard it with !vers_conditions.was_set() rather than !is_set(): set_all() sets type (flips is_set()) but not orig_type (was_set()), so is_set() would stay true across prepared-statement / stored-procedure re-executions and skip the restriction, leaving history partitions readable - rows matched then grow on each execute/call. EXPLAIN no longer shows "Using where" for such a query: correctness now comes from partition selection rather than a row_end filter.
Avoid result fluctuations with different storage engines.
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