MDEV-515 Reduce InnoDB undo logging for insert into empty table

We implement an idea that was suggested by Michael 'Monty' Widenius
in October 2017: When InnoDB is inserting into an empty table or partition,
we can write a single undo log record TRX_UNDO_EMPTY, which will cause
ROLLBACK to clear the table.

For this to work, the insert into an empty table or partition must be
covered by an exclusive table lock that will be held until the transaction
has been committed or rolled back, or the INSERT operation has been
rolled back (and the table is empty again), in lock_table_x_unlock().

Clustered index records that are covered by the TRX_UNDO_EMPTY record
will carry DB_TRX_ID=0 and DB_ROLL_PTR=1<<55, and thus they cannot
be distinguished from what MDEV-12288 leaves behind after purging the
history of row-logged operations.

Concurrent non-locking reads must be adjusted: If the read view was
created before the INSERT into an empty table, then we must continue
to imagine that the table is empty, and not try to read any records.
If the read view was created after the INSERT was committed, then
all records must be visible normally. To implement this, we introduce
the field dict_table_t::bulk_trx_id.

This special handling only applies to the very first INSERT statement
of a transaction for the empty table or partition. If a subsequent
statement in the transaction is modifying the initially empty table again,
we must enable row-level undo logging, so that we will be able to
roll back to the start of the statement in case of an error (such as
duplicate key).

INSERT IGNORE will continue to use row-level logging and locking, because
implementing it would require the ability to roll back the latest row.
Since the undo log that we write only allows us to roll back the entire
statement, we cannot support INSERT IGNORE. We will introduce a
handler::extra() parameter HA_EXTRA_IGNORE_INSERT to indicate to storage
engines that INSERT IGNORE is being executed.

In many test cases, we add an extra record to the table, so that during
the 'interesting' part of the test, row-level locking and logging will
be used.

Replicas will continue to use row-level logging and locking until
MDEV-24622 has been addressed. Likewise, this optimization will be
disabled in Galera cluster until MDEV-24623 enables it.

dict_table_t::bulk_trx_id: The latest active or committed transaction
that initiated an insert into an empty table or partition.
Protected by exclusive table lock and a clustered index leaf page latch.

ins_node_t::bulk_insert: Whether bulk insert was initiated.

trx_t::mod_tables: Use C++11 style accessors (emplace instead of insert).
Unlike earlier, this collection will cover also temporary tables.

trx_mod_table_time_t: Add start_bulk_insert(), end_bulk_insert(),
is_bulk_insert(), was_bulk_insert().

trx_undo_report_row_operation(): Before accessing any undo log pages,
invoke trx->mod_tables.emplace() in order to determine whether undo
logging was disabled, or whether this is the first INSERT and we are
supposed to write a TRX_UNDO_EMPTY record.

row_ins_clust_index_entry_low(): If we are inserting into an empty
clustered index leaf page, set the ins_node_t::bulk_insert flag for
the subsequent trx_undo_report_row_operation() call.

lock_rec_insert_check_and_lock(), lock_prdt_insert_check_and_lock():
Remove the redundant parameter 'flags' that can be checked in the caller.

btr_cur_ins_lock_and_undo(): Simplify the logic. Correctly write
DB_TRX_ID,DB_ROLL_PTR after invoking trx_undo_report_row_operation().

trx_mark_sql_stat_end(), ha_innobase::extra(HA_EXTRA_IGNORE_INSERT),
ha_innobase::external_lock(): Invoke trx_t::end_bulk_insert() so that
the next statement will not be covered by table-level undo logging.

ReadView::changes_visible(trx_id_t) const: New accessor for the case
where the trx_id_t is not read from a potentially corrupted index page
but directly from the memory. In this case, we can skip a sanity check.

row_sel(), row_sel_try_search_shortcut(), row_search_mvcc():
row_sel_try_search_shortcut_for_mysql(),
row_merge_read_clustered_index(): Check dict_table_t::bulk_trx_id.

row_sel_clust_sees(): Replaces lock_clust_rec_cons_read_sees().

lock_sec_rec_cons_read_sees(): Replaced with lower-level code.

btr_root_page_init(): Refactored from btr_create().

dict_index_t::clear(), dict_table_t::clear(): Empty an index or table,
for the ROLLBACK of an INSERT operation.

ROW_T_EMPTY, ROW_OP_EMPTY: Note a concurrent ROLLBACK of an INSERT
into an empty table.

This is joint work with Thirunarayanan Balathandayuthapani,
who created a working prototype.
Thanks to Matthias Leich for extensive testing.

1 files changed, 31 insertions, 6 deletions

diff --git a/storage/innobase/row/row0merge.cc b/storage/innobase/row/row0merge.cc
index 3c9331d9909..33990f619c6 100644
--- a/storage/innobase/row/row0merge.cc
+++ b/storage/innobase/row/row0merge.cc
@@ -1,7 +1,7 @@
 /*****************************************************************************
 
 Copyright (c) 2005, 2017, Oracle and/or its affiliates. All Rights Reserved.
-Copyright (c) 2014, 2020, MariaDB Corporation.
+Copyright (c) 2014, 2021, MariaDB Corporation.
 
 This program is free software; you can redistribute it and/or modify it under
 the terms of the GNU General Public License as published by the Free Software
@@ -1739,7 +1739,7 @@ row_merge_read_clustered_index(
 		ut_malloc_nokey(n_index * sizeof *merge_buf));
 
 	row_merge_dup_t	clust_dup = {index[0], table, col_map, 0};
-	dfield_t*	prev_fields;
+	dfield_t*	prev_fields = nullptr;
 	const ulint	n_uniq = dict_index_get_n_unique(index[0]);
 
 	ut_ad(trx->mysql_thd != NULL);
@@ -1838,6 +1838,34 @@ row_merge_read_clustered_index(
 		btr_pcur_move_to_prev_on_page(&pcur);
 	}
 
+	uint64_t n_rows = 0;
+
+	/* Check if the table is supposed to be empty for our read view.
+
+	If we read bulk_trx_id as an older transaction ID, it is not
+	incorrect to check here whether that transaction should be
+	visible to us. If bulk_trx_id is not visible to us, the table
+	must have been empty at an earlier point of time, also in our
+	read view.
+
+	An INSERT would only update bulk_trx_id in
+	row_ins_clust_index_entry_low() if the table really was empty
+	(everything had been purged), when holding a leaf page latch
+	in the clustered index (actually, the root page is the only
+	leaf page in that case).
+
+	We are holding a clustered index leaf page latch here.
+	That will obviously prevent any concurrent INSERT from
+	updating bulk_trx_id while we read it. */
+	if (!online) {
+	} else if (trx_id_t bulk_trx_id = old_table->bulk_trx_id) {
+		ut_ad(trx->read_view.is_open());
+		ut_ad(bulk_trx_id != trx->id);
+		if (!trx->read_view.changes_visible(bulk_trx_id)) {
+			goto func_exit;
+		}
+	}
+
 	if (old_table != new_table) {
 		/* The table is being rebuilt.  Identify the columns
 		that were flagged NOT NULL in the new table, so that
@@ -1884,13 +1912,10 @@ row_merge_read_clustered_index(
 		prev_fields = static_cast<dfield_t*>(
 			ut_malloc_nokey(n_uniq * sizeof *prev_fields));
 		mtuple_heap = mem_heap_create(sizeof(mrec_buf_t));
-	} else {
-		prev_fields = NULL;
 	}
 
 	mach_write_to_8(new_sys_trx_start, trx->id);
 	mach_write_to_8(new_sys_trx_end, TRX_ID_MAX);
-	uint64_t	n_rows = 0;
 
 	/* Scan the clustered index. */
 	for (;;) {
@@ -2720,7 +2745,7 @@ all_done:
 		UT_DELETE(clust_btr_bulk);
 	}
 
-	if (prev_fields != NULL) {
+	if (prev_fields) {
 		ut_free(prev_fields);
 		mem_heap_free(mtuple_heap);
 	}