MDEV-32286 ANALYZE displays a huge number of InnoDB secondary index pages_accessed

[iMineLink]

Added two commits, one for reproducing the issue cited in the ticket, and the second one with an optimization that adds a shortcut to directly fetch the clustered index leaf page with an hint (without full traversal) in case there's correlation during a non-covering secondary index scan.
The optimization self-disengages after 2 consecutive failures.
That's the price these kind of queries have to pay in terms of pages_accessed even when they don't benefit from this (maybe due to fully decorrelated secondary-to-clustered index access pattern).

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[Copilot]

Pull request overview

This PR addresses MDEV-32286 by reducing inflated pages_accessed reporting during non-covering secondary-index scans in InnoDB, introducing a fast-path that reuses the previously accessed clustered-index leaf page when access patterns show correlation.

Changes:

• Add a clustered-leaf “hint” fast-path (btr_cur_t::try_leaf_hint()) to avoid repeated root-to-leaf descents on correlated clustered lookups.
• Track and reset per-statement hint state in row_prebuilt_t (remembered leaf page + consecutive miss streak with auto-disable).
• Add an MTR test suite case for non-covering secondary index scans and update expected outputs affected by the new access pattern.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
storage/innobase/row/row0sel.cc	Attempts clustered-leaf hint before full clustered-index descent; remembers last clustered leaf page id.
storage/innobase/include/row0mysql.h	Adds per-statement state to row_prebuilt_t for clustered leaf hinting and miss streak tracking.
storage/innobase/include/btr0cur.h	Declares btr_cur_t::try_leaf_hint() API for direct hinted leaf probing.
storage/innobase/handler/ha_innodb.cc	Resets hint state in ha_innobase::reset() to scope hinting to a single statement.
storage/innobase/btr/btr0cur.cc	Implements try_leaf_hint() using non-blocking, no-I/O page acquisition and page-local search.
mysql-test/suite/innodb/t/non_covering_sec_idx_scan.test	Adds regression/repro test for pages_accessed behavior across correlated and decorrelated patterns.
mysql-test/suite/innodb/r/non_covering_sec_idx_scan.result	Captures expected output for the new test case.
mysql-test/main/rowid_filter_innodb.result	Updates expected pages_accessed values affected by the optimization.

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[Copilot]

Pull request overview

Copilot reviewed 9 out of 9 changed files in this pull request and generated 1 comment.

[iMineLink]

I reordered and adjusted the datatypes of the new row_prebuilt_t members.
Now they fit in pre-existing holes in the 3rd cacheline as verified with pahole:

### Before

$ pahole -C row_prebuilt_t build/RelWithDebInfo/storage/innobase/CMakeFiles/innobase.dir/row/row0sel.cc.o

...

struct btr_pcur_t *        pcur;                 /*   120     8 */
/* --- cacheline 2 boundary (128 bytes) --- */
struct btr_pcur_t *        clust_pcur;           /*   128     8 */
struct que_fork_t *        sel_graph;            /*   136     8 */
struct dtuple_t *          search_tuple;         /*   144     8 */
byte                       row_id[6];            /*   152     6 */

/* XXX 2 bytes hole, try to pack */

doc_id_t                   fts_doc_id;           /*   160     8 */
struct dtuple_t *          clust_ref;            /*   168     8 */
enum lock_mode             select_lock_type;     /*   176     4 */
bool                       skip_locked;          /*   180     1 */

/* XXX 3 bytes hole, try to pack */

enum lock_mode             stored_select_lock_type; /*   184     4 */

/* XXX 4 bytes hole, try to pack */

/* --- cacheline 3 boundary (192 bytes) --- */
ulint                      row_read_type;        /*   192     8 */

...

/* size: 456, cachelines: 8, members: 62 */
/* sum members: 418, holes: 8, sum holes: 34 */
/* sum bitfield members: 30 bits, bit holes: 1, sum bit holes: 2 bits */
/* last cacheline: 8 bytes */

### After

...

struct btr_pcur_t *        pcur;                 /*   120     8 */
/* --- cacheline 2 boundary (128 bytes) --- */
struct btr_pcur_t *        clust_pcur;           /*   128     8 */
struct que_fork_t *        sel_graph;            /*   136     8 */
struct dtuple_t *          search_tuple;         /*   144     8 */
byte                       row_id[6];            /*   152     6 */

/* XXX 2 bytes hole, try to pack */

doc_id_t                   fts_doc_id;           /*   160     8 */
struct dtuple_t *          clust_ref;            /*   168     8 */
enum lock_mode             select_lock_type;     /*   176     4 */
bool                       skip_locked;          /*   180     1 */
uint8_t                    clust_leaf_hint_miss_streak; /*   181     1 */

/* XXX 2 bytes hole, try to pack */

uint32_t                   clust_leaf_hint_page_no; /*   184     4 */
enum lock_mode             stored_select_lock_type; /*   188     4 */
/* --- cacheline 3 boundary (192 bytes) --- */
ulint                      row_read_type;        /*   192     8 */

...

/* size: 456, cachelines: 8, members: 64 */
/* sum members: 423, holes: 7, sum holes: 29 */
/* sum bitfield members: 30 bits, bit holes: 1, sum bit holes: 2 bits */
/* last cacheline: 8 bytes */

On a side note, it could be possible to reorder the fields in the struct to optimize its layout.