MDEV-22456 Dropping the adaptive hash index may cause DDL to lock up InnoDB

If the InnoDB buffer pool contains many pages for a table or index
that is being dropped or rebuilt, and if many of such pages are
pointed to by the adaptive hash index, dropping the adaptive hash index
may consume a lot of time.

The time-consuming operation of dropping the adaptive hash index entries
is being executed while the InnoDB data dictionary cache dict_sys is
exclusively locked.

It is not actually necessary to drop all adaptive hash index entries
at the time a table or index is being dropped or rebuilt. We can let
the LRU replacement policy of the buffer pool take care of this gradually.
For this to work, we must detach the dict_table_t and dict_index_t
objects from the main dict_sys cache, and once the last
adaptive hash index entry for the detached table is removed
(when the garbage page is evicted from the buffer pool) we can free
the dict_table_t and dict_index_t object.

Related to this, in MDEV-16283, we made ALTER TABLE...DISCARD TABLESPACE
skip both the buffer pool eviction and the drop of the adaptive hash index.
We shifted the burden to ALTER TABLE...IMPORT TABLESPACE or DROP TABLE.
We can remove the eviction from DROP TABLE. We must retain the eviction
in the ALTER TABLE...IMPORT TABLESPACE code path, so that in case the
discarded table is being re-imported with the same tablespace identifier,
the fresh data from the imported tablespace will replace any stale pages
in the buffer pool.

rpl.rpl_failed_drop_tbl_binlog: Remove the test. DROP TABLE can
no longer be interrupted inside InnoDB.

fseg_free_page(), fseg_free_step(), fseg_free_step_not_header(),
fseg_free_page_low(), fseg_free_extent(): Remove the parameter
that specifies whether the adaptive hash index should be dropped.

btr_search_lazy_free(): Lazily free an index when the last
reference to it is dropped from the adaptive hash index.

buf_pool_clear_hash_index(): Declare static, and move to the
same compilation unit with the bulk of the adaptive hash index
code.

dict_index_t::clone(), dict_index_t::clone_if_needed():
Clone an index that is being rebuilt while adaptive hash index
entries exist. The original index will be inserted into
dict_table_t::freed_indexes and dict_index_t::set_freed()
will be called.

dict_index_t::set_freed(), dict_index_t::freed(): Note that
or check whether the index has been freed. We will use the
impossible page number 1 to denote this condition.

dict_index_t::n_ahi_pages(): Replaces btr_search_info_get_ref_count().

dict_index_t::detach_columns(): Move the assignment n_fields=0
to ha_innobase_inplace_ctx::clear_added_indexes().
We must have access to the columns when freeing the
adaptive hash index. Note: dict_table_t::v_cols[] will remain
valid. If virtual columns are dropped or added, the table
definition will be reloaded in ha_innobase::commit_inplace_alter_table().

buf_page_mtr_lock(): Drop a stale adaptive hash index if needed.

We will also reduce the number of btr_get_search_latch() calls
and enclose some more code inside #ifdef BTR_CUR_HASH_ADAPT
in order to benefit cmake -DWITH_INNODB_AHI=OFF.

1 files changed, 13 insertions, 8 deletions

diff --git a/storage/innobase/btr/btr0cur.cc b/storage/innobase/btr/btr0cur.cc
index 2bf657f037f..37ba133cb0f 100644
--- a/storage/innobase/btr/btr0cur.cc
+++ b/storage/innobase/btr/btr0cur.cc
@@ -864,8 +864,7 @@ search tuple should be performed in the B-tree. InnoDB does an insert
 immediately after the cursor. Thus, the cursor may end up on a user record,
 or on a page infimum record. */
 dberr_t
-btr_cur_search_to_nth_level(
-/*========================*/
+btr_cur_search_to_nth_level_func(
 	dict_index_t*	index,	/*!< in: index */
 	ulint		level,	/*!< in: the tree level of search */
 	const dtuple_t*	tuple,	/*!< in: data tuple; NOTE: n_fields_cmp in
@@ -887,10 +886,12 @@ btr_cur_search_to_nth_level(
 				to protect the record! */
 	btr_cur_t*	cursor, /*!< in/out: tree cursor; the cursor page is
 				s- or x-latched, but see also above! */
+#ifdef BTR_CUR_HASH_ADAPT
 	ulint		has_search_latch,
 				/*!< in: info on the latch mode the
 				caller currently has on search system:
 				RW_S_LATCH, or 0 */
+#endif /* BTR_CUR_HASH_ADAPT */
 	const char*	file,	/*!< in: file name */
 	unsigned	line,	/*!< in: line where called */
 	mtr_t*		mtr,	/*!< in: mtr */
@@ -1053,6 +1054,7 @@ btr_cur_search_to_nth_level(
 	}
 
 #ifdef BTR_CUR_HASH_ADAPT
+	rw_lock_t* const search_latch = btr_get_search_latch(index);
 
 # ifdef UNIV_SEARCH_PERF_STAT
 	info->n_searches++;
@@ -1073,8 +1075,7 @@ btr_cur_search_to_nth_level(
 	    will have to check it again. */
 	    && btr_search_enabled
 	    && !modify_external
-	    && rw_lock_get_writer(btr_get_search_latch(index))
-	    == RW_LOCK_NOT_LOCKED
+	    && rw_lock_get_writer(search_latch) == RW_LOCK_NOT_LOCKED
 	    && btr_search_guess_on_hash(index, info, tuple, mode,
 					latch_mode, cursor,
 					has_search_latch, mtr)) {
@@ -1098,10 +1099,12 @@ btr_cur_search_to_nth_level(
 	/* If the hash search did not succeed, do binary search down the
 	tree */
 
+#ifdef BTR_CUR_HASH_ADAPT
 	if (has_search_latch) {
 		/* Release possible search latch to obey latching order */
-		btr_search_s_unlock(index);
+		rw_lock_s_unlock(search_latch);
 	}
+#endif /* BTR_CUR_HASH_ADAPT */
 
 	/* Store the position of the tree latch we push to mtr so that we
 	know how to release it when we have latched leaf node(s) */
@@ -2155,9 +2158,11 @@ func_exit:
 		ut_free(prev_tree_savepoints);
 	}
 
+#ifdef BTR_CUR_HASH_ADAPT
 	if (has_search_latch) {
-		btr_search_s_lock(index);
+		rw_lock_s_lock(search_latch);
 	}
+#endif /* BTR_CUR_HASH_ADAPT */
 
 	if (mbr_adj) {
 		/* remember that we will need to adjust parent MBR */
@@ -5746,7 +5751,7 @@ btr_estimate_n_rows_in_range_low(
 		btr_cur_search_to_nth_level(index, 0, tuple1, mode1,
 					    BTR_SEARCH_LEAF | BTR_ESTIMATE,
 					    &cursor, 0,
-					    __FILE__, __LINE__, &mtr);
+					    __FILE__, __LINE__, &mtr, 0);
 
 		ut_ad(!page_rec_is_infimum(btr_cur_get_rec(&cursor)));
 
@@ -5800,7 +5805,7 @@ btr_estimate_n_rows_in_range_low(
 		btr_cur_search_to_nth_level(index, 0, tuple2, mode2,
 					    BTR_SEARCH_LEAF | BTR_ESTIMATE,
 					    &cursor, 0,
-					    __FILE__, __LINE__, &mtr);
+					    __FILE__, __LINE__, &mtr, 0);
 
 		const rec_t*	rec = btr_cur_get_rec(&cursor);