MDEV-25581 Allow user thread to do InnoDB fts cache sync

Problem:
========
  InnoDB FTS requesting the fts sync of the table once the fts
cache size reaches 1/10 of innodb_ft_cache_size. But fts_sync()
releases cache lock when writing the word. By doing this, InnoDB
insert thread increases the innodb fts cache memory and
SYNC operation will take more time to complete.

Solution:
=========
  Remove the fts sync operation(FTS_MSG_SYNC_TABLE) from
the fts optimize background thread. Instead of that,
allow user thread to sync the InnoDB fts cache when
the cache size exceeds 512 kb. User thread holds
cache lock while doing cache syncing, it make sure that
other threads doesn't add the docs into the cache.

Removed FTS_MSG_SYNC_TABLE and its related function
because we do remove the FTS_MSG_SYNC_TABLE message
itself.

Removed fts_sync_index_check() and all related
function because other threads doesn't add while
cache operation going on.

11 files changed, 82 insertions, 395 deletions

diff --git a/mysql-test/suite/innodb_fts/r/concurrent_insert.result b/mysql-test/suite/innodb_fts/r/concurrent_insert.result
index e91ea02b1de..3cb48d22df1 100644
--- a/mysql-test/suite/innodb_fts/r/concurrent_insert.result
+++ b/mysql-test/suite/innodb_fts/r/concurrent_insert.result
@@ -19,7 +19,7 @@ INSERT INTO t2 VALUES('mariadb');
 connection default;
 SET @saved_dbug = @@GLOBAL.debug_dbug;
 SET GLOBAL debug_dbug ='+d,fts_instrument_sync_request,ib_optimize_wq_hang';
-SET DEBUG_SYNC= 'fts_instrument_sync_request
+SET DEBUG_SYNC= 'fts_sync_end
 		 SIGNAL drop_index_start WAIT_FOR sync_op';
 INSERT INTO t1 VALUES('Keyword');
 connect con1,localhost,root,,,;
diff --git a/mysql-test/suite/innodb_fts/r/sync.result b/mysql-test/suite/innodb_fts/r/sync.result
index 928efffdb21..74a5d2f13fb 100644
--- a/mysql-test/suite/innodb_fts/r/sync.result
+++ b/mysql-test/suite/innodb_fts/r/sync.result
@@ -11,19 +11,19 @@ INSERT INTO t1(title) VALUES('database');
 connection con1;
 SET @old_dbug = @@SESSION.debug_dbug;
 SET debug_dbug = '+d,fts_instrument_sync_debug';
-SET DEBUG_SYNC= 'fts_write_node SIGNAL written WAIT_FOR selected';
+SET DEBUG_SYNC= 'fts_sync_end SIGNAL written WAIT_FOR selected';
 INSERT INTO t1(title) VALUES('mysql database');
 connection default;
 SET DEBUG_SYNC= 'now WAIT_FOR written';
 SET GLOBAL innodb_ft_aux_table="test/t1";
 SELECT * FROM INFORMATION_SCHEMA.INNODB_FT_INDEX_CACHE;
 WORD	FIRST_DOC_ID	LAST_DOC_ID	DOC_COUNT	DOC_ID	POSITION
+SELECT * FROM INFORMATION_SCHEMA.INNODB_FT_INDEX_TABLE;
+WORD	FIRST_DOC_ID	LAST_DOC_ID	DOC_COUNT	DOC_ID	POSITION
 database	2	3	2	2	0
 database	2	3	2	3	6
 mysql	1	3	2	1	0
 mysql	1	3	2	3	0
-SELECT * FROM INFORMATION_SCHEMA.INNODB_FT_INDEX_TABLE;
-WORD	FIRST_DOC_ID	LAST_DOC_ID	DOC_COUNT	DOC_ID	POSITION
 SET GLOBAL innodb_ft_aux_table=default;
 SELECT * FROM t1 WHERE MATCH(title) AGAINST('mysql database');
 FTS_DOC_ID	title
@@ -59,7 +59,7 @@ INSERT INTO t1(title) VALUES('mysql');
 INSERT INTO t1(title) VALUES('database');
 connection con1;
 SET debug_dbug = '+d,fts_instrument_sync_debug';
-SET DEBUG_SYNC= 'fts_write_node SIGNAL written WAIT_FOR inserted';
+SET DEBUG_SYNC= 'fts_sync_end SIGNAL written WAIT_FOR inserted';
 INSERT INTO t1(title) VALUES('mysql database');
 connection default;
 SET DEBUG_SYNC= 'now WAIT_FOR written';
@@ -70,14 +70,14 @@ SET debug_dbug = @old_dbug;
 SET GLOBAL innodb_ft_aux_table="test/t1";
 SELECT * FROM INFORMATION_SCHEMA.INNODB_FT_INDEX_CACHE;
 WORD	FIRST_DOC_ID	LAST_DOC_ID	DOC_COUNT	DOC_ID	POSITION
+database	4	4	1	4	6
+mysql	4	4	1	4	0
 SELECT * FROM INFORMATION_SCHEMA.INNODB_FT_INDEX_TABLE;
 WORD	FIRST_DOC_ID	LAST_DOC_ID	DOC_COUNT	DOC_ID	POSITION
 database	2	3	2	2	0
 database	2	3	2	3	6
-database	4	4	1	4	6
-mysql	1	4	3	1	0
-mysql	1	4	3	3	0
-mysql	1	4	3	4	0
+mysql	1	3	2	1	0
+mysql	1	3	2	3	0
 SET GLOBAL innodb_ft_aux_table=default;
 SELECT * FROM t1 WHERE MATCH(title) AGAINST('mysql database');
 FTS_DOC_ID	title
diff --git a/mysql-test/suite/innodb_fts/r/sync_block.result b/mysql-test/suite/innodb_fts/r/sync_block.result
index 65bee127e80..c105a3d3b12 100644
--- a/mysql-test/suite/innodb_fts/r/sync_block.result
+++ b/mysql-test/suite/innodb_fts/r/sync_block.result
@@ -30,6 +30,7 @@ connection con1;
 connection con2;
 /* conneciton con2 */ SELECT * FROM t1 WHERE MATCH(title) AGAINST('mysql database');
 FTS_DOC_ID	title
+1	mysql database
 connection default;
 # make con1 & con2 show up in mysql.slow_log
 SELECT SLEEP(2);
@@ -39,41 +40,11 @@ SLEEP(2)
 SELECT sql_text FROM mysql.slow_log WHERE query_time >= '00:00:02';
 sql_text
 INSERT INTO t1(title) VALUES('mysql database')
+SELECT * FROM t1 WHERE MATCH(title) AGAINST('mysql database')
 SET GLOBAL debug_dbug = @old_debug;
 TRUNCATE TABLE mysql.slow_log;
 DROP TABLE t1;
-# Case 2: Sync blocks DML(insert) on other tables.
-CREATE TABLE t1 (
-FTS_DOC_ID BIGINT UNSIGNED AUTO_INCREMENT NOT NULL PRIMARY KEY,
-title VARCHAR(200),
-FULLTEXT(title)
-) ENGINE = InnoDB;
-CREATE TABLE t2(id INT);
-connection con1;
-SET GLOBAL debug_dbug='+d,fts_instrument_sync_request,fts_instrument_sync_sleep';
-SET DEBUG_SYNC= 'fts_instrument_sync_request SIGNAL begin WAIT_FOR continue';
-INSERT INTO t1(title) VALUES('mysql database');
-connection con2;
-SET DEBUG_SYNC= 'now WAIT_FOR begin';
-INSERT INTO t2 VALUES(1);
-connection default;
-SET DEBUG_SYNC= 'now SIGNAL continue';
-connection con1;
-/* connection con1 */ INSERT INTO t1(title) VALUES('mysql database');
-connection con2;
-/* conneciton con2 */ INSERT INTO t2 VALUES(1);
-connection default;
-SET DEBUG_SYNC = 'RESET';
-# make con1 & con2 show up in mysql.slow_log
-SELECT SLEEP(2);
-SLEEP(2)
-0
-# slow log results should be empty here.
-SELECT sql_text FROM mysql.slow_log WHERE query_time >= '00:00:02';
-sql_text
-SET GLOBAL debug_dbug = @old_debug;
-TRUNCATE TABLE mysql.slow_log;
-DROP TABLE t1,t2;
+SET DEBUG_SYNC=RESET;
 disconnect con1;
 disconnect con2;
 # Restore slow log settings.
diff --git a/mysql-test/suite/innodb_fts/t/concurrent_insert.test b/mysql-test/suite/innodb_fts/t/concurrent_insert.test
index 35debd87cea..d70fc0f63c4 100644
--- a/mysql-test/suite/innodb_fts/t/concurrent_insert.test
+++ b/mysql-test/suite/innodb_fts/t/concurrent_insert.test
@@ -31,7 +31,7 @@ INSERT INTO t2 VALUES('mariadb');
 connection default;
 SET @saved_dbug = @@GLOBAL.debug_dbug;
 SET GLOBAL debug_dbug ='+d,fts_instrument_sync_request,ib_optimize_wq_hang';
-SET DEBUG_SYNC= 'fts_instrument_sync_request
+SET DEBUG_SYNC= 'fts_sync_end
 		 SIGNAL drop_index_start WAIT_FOR sync_op';
 send INSERT INTO t1 VALUES('Keyword');
 
diff --git a/mysql-test/suite/innodb_fts/t/sync.test b/mysql-test/suite/innodb_fts/t/sync.test
index f16953ba09f..92c21c9ac83 100644
--- a/mysql-test/suite/innodb_fts/t/sync.test
+++ b/mysql-test/suite/innodb_fts/t/sync.test
@@ -26,7 +26,7 @@ connection con1;
 SET @old_dbug = @@SESSION.debug_dbug;
 SET debug_dbug = '+d,fts_instrument_sync_debug';
 
-SET DEBUG_SYNC= 'fts_write_node SIGNAL written WAIT_FOR selected';
+SET DEBUG_SYNC= 'fts_sync_end SIGNAL written WAIT_FOR selected';
 
 send INSERT INTO t1(title) VALUES('mysql database');
 
@@ -73,7 +73,7 @@ connection con1;
 
 SET debug_dbug = '+d,fts_instrument_sync_debug';
 
-SET DEBUG_SYNC= 'fts_write_node SIGNAL written WAIT_FOR inserted';
+SET DEBUG_SYNC= 'fts_sync_end SIGNAL written WAIT_FOR inserted';
 
 send INSERT INTO t1(title) VALUES('mysql database');
 
diff --git a/mysql-test/suite/innodb_fts/t/sync_block.test b/mysql-test/suite/innodb_fts/t/sync_block.test
index 895d2ba8a59..705567296f7 100644
--- a/mysql-test/suite/innodb_fts/t/sync_block.test
+++ b/mysql-test/suite/innodb_fts/t/sync_block.test
@@ -65,53 +65,7 @@ SET GLOBAL debug_dbug = @old_debug;
 TRUNCATE TABLE mysql.slow_log;
 
 DROP TABLE t1;
-
---echo # Case 2: Sync blocks DML(insert) on other tables.
-CREATE TABLE t1 (
-        FTS_DOC_ID BIGINT UNSIGNED AUTO_INCREMENT NOT NULL PRIMARY KEY,
-        title VARCHAR(200),
-        FULLTEXT(title)
-) ENGINE = InnoDB;
-
-CREATE TABLE t2(id INT);
-
-connection con1;
-
-SET GLOBAL debug_dbug='+d,fts_instrument_sync_request,fts_instrument_sync_sleep';
-
-SET DEBUG_SYNC= 'fts_instrument_sync_request SIGNAL begin WAIT_FOR continue';
-
-send INSERT INTO t1(title) VALUES('mysql database');
-
-connection con2;
-
-SET DEBUG_SYNC= 'now WAIT_FOR begin';
-
-send INSERT INTO t2 VALUES(1);
-
-connection default;
-SET DEBUG_SYNC= 'now SIGNAL continue';
-
-connection con1;
---echo /* connection con1 */ INSERT INTO t1(title) VALUES('mysql database');
---reap
-
-connection con2;
---echo /* conneciton con2 */ INSERT INTO t2 VALUES(1);
---reap
-
-connection default;
-SET DEBUG_SYNC = 'RESET';
--- echo # make con1 & con2 show up in mysql.slow_log
-SELECT SLEEP(2);
--- echo # slow log results should be empty here.
-SELECT sql_text FROM mysql.slow_log WHERE query_time >= '00:00:02';
-
-SET GLOBAL debug_dbug = @old_debug;
-TRUNCATE TABLE mysql.slow_log;
-
-DROP TABLE t1,t2;
-
+SET DEBUG_SYNC=RESET;
 disconnect con1;
 disconnect con2;
 
diff --git a/storage/innobase/fts/fts0fts.cc b/storage/innobase/fts/fts0fts.cc
index 0a82dc39303..afbb904d5c5 100644
--- a/storage/innobase/fts/fts0fts.cc
+++ b/storage/innobase/fts/fts0fts.cc
@@ -38,6 +38,22 @@ Full Text Search interface
 #include "dict0stats.h"
 #include "btr0pcur.h"
 
+/** The SYNC state of the cache. There is one instance of this struct
+associated with each ADD thread. */
+struct fts_sync_t {
+        /** Transaction used for SYNCing the cache to disk */
+        trx_t   *trx;
+        /** Table with FTS index(es) */
+        dict_table_t    *table;
+        /** Max size in bytes of the cache */
+        ulint           max_cache_size;
+        /** The doc id at which the cache was noted as being
+        full, we use this to set the upper_limit field */
+        doc_id_t        max_doc_id;
+        /** SYNC start time; only used if fts_enable_diag_print */
+        time_t          start_time;
+};
+
 static const ulint FTS_MAX_ID_LEN = 32;
 
 /** Column name from the FTS config table */
@@ -185,15 +201,8 @@ struct fts_tokenize_param_t {
 /** Run SYNC on the table, i.e., write out data from the cache to the
 FTS auxiliary INDEX table and clear the cache at the end.
 @param[in,out]	sync		sync state
-@param[in]	unlock_cache	whether unlock cache lock when write node
-@param[in]	wait		whether wait when a sync is in progress
 @return DB_SUCCESS if all OK */
-static
-dberr_t
-fts_sync(
-	fts_sync_t*	sync,
-	bool		unlock_cache,
-	bool		wait);
+static dberr_t fts_sync(fts_sync_t *sync);
 
 /****************************************************************//**
 Release all resources help by the words rb tree e.g., the node ilist. */
@@ -266,7 +275,6 @@ fts_cache_destroy(fts_cache_t* cache)
 	mysql_mutex_destroy(&cache->init_lock);
 	mysql_mutex_destroy(&cache->deleted_lock);
 	mysql_mutex_destroy(&cache->doc_id_lock);
-	pthread_cond_destroy(&cache->sync->cond);
 
 	if (cache->stopword_info.cached_stopword) {
 		rbt_free(cache->stopword_info.cached_stopword);
@@ -540,7 +548,6 @@ fts_index_cache_init(
 
 	for (i = 0; i < FTS_NUM_AUX_INDEX; ++i) {
 		ut_a(index_cache->ins_graph[i] == NULL);
-		ut_a(index_cache->sel_graph[i] == NULL);
 	}
 }
 
@@ -610,7 +617,6 @@ fts_cache_create(
 		mem_heap_zalloc(heap, sizeof(fts_sync_t)));
 
 	cache->sync->table = table;
-	pthread_cond_init(&cache->sync->cond, nullptr);
 
 	/* Create the index cache vector that will hold the inverted indexes. */
 	cache->indexes = ib_vector_create(
@@ -935,10 +941,6 @@ fts_cache_index_cache_create(
 		mem_heap_zalloc(static_cast<mem_heap_t*>(
 			cache->self_heap->arg), n_bytes));
 
-	index_cache->sel_graph = static_cast<que_t**>(
-		mem_heap_zalloc(static_cast<mem_heap_t*>(
-			cache->self_heap->arg), n_bytes));
-
 	fts_index_cache_init(cache->sync_heap, index_cache);
 
 	if (cache->get_docs) {
@@ -1012,13 +1014,6 @@ fts_cache_clear(
 
 				index_cache->ins_graph[j] = NULL;
 			}
-
-			if (index_cache->sel_graph[j] != NULL) {
-
-				que_graph_free(index_cache->sel_graph[j]);
-
-				index_cache->sel_graph[j] = NULL;
-			}
 		}
 
 		index_cache->doc_stats = NULL;
@@ -1311,8 +1306,7 @@ fts_cache_add_doc(
 				ib_vector_last(word->nodes));
 		}
 
-		if (fts_node == NULL || fts_node->synced
-		    || fts_node->ilist_size > FTS_ILIST_MAX_SIZE
+		if (!fts_node || fts_node->ilist_size > FTS_ILIST_MAX_SIZE
 		    || doc_id < fts_node->last_doc_id) {
 
 			fts_node = static_cast<fts_node_t*>(
@@ -3284,7 +3278,7 @@ fts_add_doc_from_tuple(
 
                        if (cache->total_size > fts_max_cache_size / 5
                            || fts_need_sync) {
-                               fts_sync(cache->sync, true, false);
+                               fts_sync(cache->sync);
                        }
 
                        mtr_start(&mtr);
@@ -3444,42 +3438,34 @@ fts_add_doc_by_id(
 					get_doc->index_cache,
 					doc_id, doc.tokens);
 
-				bool	need_sync = !cache->sync->in_progress
-					&& (fts_need_sync
-					    || (cache->total_size
-						- cache->total_size_at_sync)
-					    > fts_max_cache_size / 10);
-				if (need_sync) {
-					cache->total_size_at_sync =
-						cache->total_size;
-				}
+				/** FTS cache sync should happen
+				frequently. Because user thread
+				shouldn't hold the cache lock for
+				longer time. So cache should sync
+				whenever cache size exceeds 512 KB */
+				bool	need_sync =
+					cache->total_size > 512*1024;
 
 				mysql_mutex_unlock(&table->fts->cache->lock);
 
 				DBUG_EXECUTE_IF(
 					"fts_instrument_sync",
-					fts_optimize_request_sync_table(table);
-					mysql_mutex_lock(&cache->lock);
-					if (cache->sync->in_progress)
-						my_cond_wait(
-							&cache->sync->cond,
-							&cache->lock.m_mutex);
-					mysql_mutex_unlock(&cache->lock);
+					fts_sync_table(table);
 				);
 
 				DBUG_EXECUTE_IF(
 					"fts_instrument_sync_debug",
-					fts_sync(cache->sync, true, true);
+					fts_sync(cache->sync);
 				);
 
 				DEBUG_SYNC_C("fts_instrument_sync_request");
 				DBUG_EXECUTE_IF(
 					"fts_instrument_sync_request",
-					fts_optimize_request_sync_table(table);
+					need_sync= true;
 				);
 
 				if (need_sync) {
-					fts_optimize_request_sync_table(table);
+					fts_sync_table(table);
 				}
 
 				mtr_start(&mtr);
@@ -3846,15 +3832,13 @@ static MY_ATTRIBUTE((nonnull, warn_unused_result))
 dberr_t
 fts_sync_write_words(
 	trx_t*			trx,
-	fts_index_cache_t*	index_cache,
-	bool			unlock_cache)
+	fts_index_cache_t*	index_cache)
 {
 	fts_table_t	fts_table;
 	ulint		n_nodes = 0;
 	ulint		n_words = 0;
 	const ib_rbt_node_t* rbt_node;
 	dberr_t		error = DB_SUCCESS;
-	ibool		print_error = FALSE;
 	dict_table_t*	table = index_cache->index->table;
 
 	FTS_INIT_INDEX_TABLE(
@@ -3885,53 +3869,35 @@ fts_sync_write_words(
 
 		fts_table.suffix = fts_get_suffix(selected);
 
-		/* We iterate over all the nodes even if there was an error */
 		for (i = 0; i < ib_vector_size(word->nodes); ++i) {
 
 			fts_node_t* fts_node = static_cast<fts_node_t*>(
 				ib_vector_get(word->nodes, i));
 
-			if (fts_node->synced) {
-				continue;
-			} else {
-				fts_node->synced = true;
-			}
-
-			/*FIXME: we need to handle the error properly. */
-			if (error == DB_SUCCESS) {
-				if (unlock_cache) {
-					mysql_mutex_unlock(
-						&table->fts->cache->lock);
-				}
-
-				error = fts_write_node(
-					trx,
-					&index_cache->ins_graph[selected],
-					&fts_table, &word->text, fts_node);
+			error = fts_write_node(
+				trx, &index_cache->ins_graph[selected],
+				&fts_table, &word->text, fts_node);
 
-				DEBUG_SYNC_C("fts_write_node");
-				DBUG_EXECUTE_IF("fts_write_node_crash",
+			DEBUG_SYNC_C("fts_write_node");
+			DBUG_EXECUTE_IF("fts_write_node_crash",
 					DBUG_SUICIDE(););
 
-				DBUG_EXECUTE_IF(
-					"fts_instrument_sync_sleep",
+			DBUG_EXECUTE_IF("fts_instrument_sync_sleep",
 					std::this_thread::sleep_for(
 						std::chrono::seconds(1)););
 
-				if (unlock_cache) {
-					mysql_mutex_lock(
-						&table->fts->cache->lock);
-				}
+			if (error != DB_SUCCESS) {
+				goto err_exit;
 			}
 		}
 
 		n_nodes += ib_vector_size(word->nodes);
 
-		if (UNIV_UNLIKELY(error != DB_SUCCESS) && !print_error) {
+		if (UNIV_UNLIKELY(error != DB_SUCCESS)) {
+err_exit:
 			ib::error() << "(" << error << ") writing"
 				" word node to FTS auxiliary index table "
 				<< table->name;
-			print_error = TRUE;
 		}
 	}
 
@@ -3990,58 +3956,7 @@ fts_sync_index(
 
 	ut_ad(rbt_validate(index_cache->words));
 
-	return(fts_sync_write_words(trx, index_cache, sync->unlock_cache));
-}
-
-/** Check if index cache has been synced completely
-@param[in,out]	index_cache	index cache
-@return true if index is synced, otherwise false. */
-static
-bool
-fts_sync_index_check(
-	fts_index_cache_t*	index_cache)
-{
-	const ib_rbt_node_t*	rbt_node;
-
-	for (rbt_node = rbt_first(index_cache->words);
-	     rbt_node != NULL;
-	     rbt_node = rbt_next(index_cache->words, rbt_node)) {
-
-		fts_tokenizer_word_t*	word;
-		word = rbt_value(fts_tokenizer_word_t, rbt_node);
-
-		fts_node_t*	fts_node;
-		fts_node = static_cast<fts_node_t*>(ib_vector_last(word->nodes));
-
-		if (!fts_node->synced) {
-			return(false);
-		}
-	}
-
-	return(true);
-}
-
-/** Reset synced flag in index cache when rollback
-@param[in,out]	index_cache	index cache */
-static
-void
-fts_sync_index_reset(
-	fts_index_cache_t*	index_cache)
-{
-	const ib_rbt_node_t*	rbt_node;
-
-	for (rbt_node = rbt_first(index_cache->words);
-	     rbt_node != NULL;
-	     rbt_node = rbt_next(index_cache->words, rbt_node)) {
-
-		fts_tokenizer_word_t*	word;
-		word = rbt_value(fts_tokenizer_word_t, rbt_node);
-
-		fts_node_t*	fts_node;
-		fts_node = static_cast<fts_node_t*>(ib_vector_last(word->nodes));
-
-		fts_node->synced = false;
-	}
+	return(fts_sync_write_words(trx, index_cache));
 }
 
 /** Commit the SYNC, change state of processed doc ids etc.
@@ -4074,14 +3989,14 @@ fts_sync_commit(
 			sync, cache->deleted_doc_ids);
 	}
 
-	/* We need to do this within the deleted lock since fts_delete() can
-	attempt to add a deleted doc id to the cache deleted id array. */
-	fts_cache_clear(cache);
-	DEBUG_SYNC_C("fts_deleted_doc_ids_clear");
-	fts_cache_init(cache);
-	mysql_mutex_unlock(&cache->lock);
-
 	if (UNIV_LIKELY(error == DB_SUCCESS)) {
+		/* We need to do this within the deleted lock
+		since fts_delete() can attempt to add a deleted
+		doc id to the cache deleted id array. */
+		fts_cache_clear(cache);
+		DEBUG_SYNC_C("fts_deleted_doc_ids_clear");
+		fts_cache_init(cache);
+		mysql_mutex_unlock(&cache->lock);
 		fts_sql_commit(trx);
 	} else {
 		fts_sql_rollback(trx);
@@ -4123,10 +4038,6 @@ fts_sync_rollback(
 		index_cache = static_cast<fts_index_cache_t*>(
 			ib_vector_get(cache->indexes, i));
 
-		/* Reset synced flag so nodes will not be skipped
-		in the next sync, see fts_sync_write_words(). */
-		fts_sync_index_reset(index_cache);
-
 		for (j = 0; fts_index_selector[j].value; ++j) {
 
 			if (index_cache->ins_graph[j] != NULL) {
@@ -4135,13 +4046,6 @@ fts_sync_rollback(
 
 				index_cache->ins_graph[j] = NULL;
 			}
-
-			if (index_cache->sel_graph[j] != NULL) {
-
-				que_graph_free(index_cache->sel_graph[j]);
-
-				index_cache->sel_graph[j] = NULL;
-			}
 		}
 	}
 
@@ -4160,12 +4064,7 @@ FTS auxiliary INDEX table and clear the cache at the end.
 @param[in]	unlock_cache	whether unlock cache lock when write node
 @param[in]	wait		whether wait when a sync is in progress
 @return DB_SUCCESS if all OK */
-static
-dberr_t
-fts_sync(
-	fts_sync_t*	sync,
-	bool		unlock_cache,
-	bool		wait)
+static dberr_t fts_sync(fts_sync_t *sync)
 {
 	if (srv_read_only_mode) {
 		return DB_READ_ONLY;
@@ -4176,33 +4075,13 @@ fts_sync(
 	fts_cache_t*	cache = sync->table->fts->cache;
 
 	mysql_mutex_lock(&cache->lock);
-
-	/* Check if cache is being synced.
-	Note: we release cache lock in fts_sync_write_words() to
-	avoid long wait for the lock by other threads. */
-	if (sync->in_progress) {
-		if (!wait) {
-			mysql_mutex_unlock(&cache->lock);
-			return(DB_SUCCESS);
-		}
-		do {
-			my_cond_wait(&sync->cond, &cache->lock.m_mutex);
-		} while (sync->in_progress);
-	}
-
-	sync->unlock_cache = unlock_cache;
-	sync->in_progress = true;
-
 	DEBUG_SYNC_C("fts_sync_begin");
 	fts_sync_begin(sync);
 
-begin_sync:
 	const size_t fts_cache_size= fts_max_cache_size;
 	if (cache->total_size > fts_cache_size) {
 		/* Avoid the case: sync never finish when
 		insert/update keeps comming. */
-		ut_ad(sync->unlock_cache);
-		sync->unlock_cache = false;
 		ib::warn() << "Total InnoDB FTS size "
 			<< cache->total_size << " for the table "
 			<< cache->sync->table->name
@@ -4226,52 +4105,23 @@ begin_sync:
 		error = fts_sync_index(sync, index_cache);
 
 		if (error != DB_SUCCESS) {
-			goto end_sync;
-		}
-
-		if (!sync->unlock_cache
-		    && cache->total_size < fts_max_cache_size) {
-			/* Reset the unlock cache if the value
-			is less than innodb_ft_cache_size */
-			sync->unlock_cache = true;
+			goto err_exit;
 		}
 	}
 
 	DBUG_EXECUTE_IF("fts_instrument_sync_interrupted",
-			sync->interrupted = true;
 			error = DB_INTERRUPTED;
-			goto end_sync;
+			goto err_exit;
 	);
 
-	/* Make sure all the caches are synced. */
-	for (i = 0; i < ib_vector_size(cache->indexes); ++i) {
-		fts_index_cache_t*	index_cache;
-
-		index_cache = static_cast<fts_index_cache_t*>(
-			ib_vector_get(cache->indexes, i));
-
-		if (index_cache->index->to_be_dropped
-		    || fts_sync_index_check(index_cache)) {
-			continue;
-		}
-
-		goto begin_sync;
-	}
-
-end_sync:
-	if (error == DB_SUCCESS && !sync->interrupted) {
+	if (error == DB_SUCCESS) {
 		error = fts_sync_commit(sync);
 	} else {
+err_exit:
 		fts_sync_rollback(sync);
+		return error;
 	}
 
-	mysql_mutex_lock(&cache->lock);
-	ut_ad(sync->in_progress);
-	sync->interrupted = false;
-	sync->in_progress = false;
-	pthread_cond_broadcast(&sync->cond);
-	mysql_mutex_unlock(&cache->lock);
-
 	/* We need to check whether an optimize is required, for that
 	we make copies of the two variables that control the trigger. These
 	variables can change behind our back and we don't want to hold the
@@ -4283,6 +4133,7 @@ end_sync:
 
 	mysql_mutex_unlock(&cache->deleted_lock);
 
+	DEBUG_SYNC_C("fts_sync_end");
 	return(error);
 }
 
@@ -4291,12 +4142,12 @@ FTS auxiliary INDEX table and clear the cache at the end.
 @param[in,out]	table		fts table
 @param[in]	wait		whether wait for existing sync to finish
 @return DB_SUCCESS on success, error code on failure. */
-dberr_t fts_sync_table(dict_table_t* table, bool wait)
+dberr_t fts_sync_table(dict_table_t* table)
 {
   ut_ad(table->fts);
 
   return table->space && !table->corrupted && table->fts->cache
-    ? fts_sync(table->fts->cache->sync, !wait, wait)
+    ? fts_sync(table->fts->cache->sync)
     : DB_SUCCESS;
 }
 
diff --git a/storage/innobase/fts/fts0opt.cc b/storage/innobase/fts/fts0opt.cc
index 030dc438193..9cc56f184fd 100644
--- a/storage/innobase/fts/fts0opt.cc
+++ b/storage/innobase/fts/fts0opt.cc
@@ -83,9 +83,8 @@ enum fts_msg_type_t {
 	FTS_MSG_ADD_TABLE,		/*!< Add table to the optimize thread's
 					work queue */
 
-	FTS_MSG_DEL_TABLE,		/*!< Remove a table from the optimize
+	FTS_MSG_DEL_TABLE		/*!< Remove a table from the optimize
 					threads work queue */
-	FTS_MSG_SYNC_TABLE		/*!< Sync fts cache of a table */
 };
 
 /** Compressed list of words that have been read from FTS INDEX
@@ -2625,36 +2624,6 @@ fts_optimize_remove_table(
   mysql_mutex_unlock(&fts_optimize_wq->mutex);
 }
 
-/** Send sync fts cache for the table.
-@param[in]	table	table to sync */
-void
-fts_optimize_request_sync_table(
-	dict_table_t*	table)
-{
-	/* if the optimize system not yet initialized, return */
-	if (!fts_optimize_wq) {
-		return;
-	}
-
-	mysql_mutex_lock(&fts_optimize_wq->mutex);
-
-	/* FTS optimizer thread is already exited */
-	if (fts_opt_start_shutdown) {
-		ib::info() << "Try to sync table " << table->name
-			<< " after FTS optimize thread exiting.";
-	} else if (table->fts->sync_message) {
-		/* If the table already has SYNC message in
-		fts_optimize_wq queue then ignore it */
-	} else {
-		add_msg(fts_optimize_create_msg(FTS_MSG_SYNC_TABLE, table));
-		table->fts->sync_message = true;
-		DBUG_EXECUTE_IF("fts_optimize_wq_count_check",
-				DBUG_ASSERT(fts_optimize_wq->length <= 1000););
-	}
-
-	mysql_mutex_unlock(&fts_optimize_wq->mutex);
-}
-
 /** Add a table to fts_slots if it doesn't already exist. */
 static bool fts_optimize_new_table(dict_table_t* table)
 {
@@ -2796,7 +2765,8 @@ static void fts_optimize_sync_table(dict_table_t *table,
 
   if (sync_table->fts && sync_table->fts->cache && sync_table->is_accessible())
   {
-    fts_sync_table(sync_table, false);
+    fts_sync_table(sync_table);
+
     if (process_message)
     {
       mysql_mutex_lock(&fts_optimize_wq->mutex);
@@ -2896,24 +2866,6 @@ retry_later:
 					--n_tables;
 				}
 				break;
-
-			case FTS_MSG_SYNC_TABLE:
-				if (UNIV_UNLIKELY(wsrep_sst_disable_writes)) {
-					add_msg(msg);
-					goto retry_later;
-				}
-
-				DBUG_EXECUTE_IF(
-					"fts_instrument_msg_sync_sleep",
-					std::this_thread::sleep_for(
-						std::chrono::milliseconds(
-							300)););
-
-				fts_optimize_sync_table(
-					static_cast<dict_table_t*>(msg->ptr),
-					true);
-				break;
-
 			default:
 				ut_error;
 			}
@@ -3046,7 +2998,7 @@ void fts_sync_during_ddl(dict_table_t* table)
   if (!sync_message)
     return;
 
-  fts_sync_table(table, false);
+  fts_sync_table(table);
 
   mysql_mutex_lock(&fts_optimize_wq->mutex);
   table->fts->sync_message = false;
diff --git a/storage/innobase/handler/handler0alter.cc b/storage/innobase/handler/handler0alter.cc
index 57eecd47ebb..19b6407f525 100644
--- a/storage/innobase/handler/handler0alter.cc
+++ b/storage/innobase/handler/handler0alter.cc
@@ -11415,12 +11415,8 @@ foreign_fail:
 		ut_d(dict_table_check_for_dup_indexes(
 			     ctx->new_table, CHECK_ABORTED_OK));
 
-#ifdef UNIV_DEBUG
-		if (!(ctx->new_table->fts != NULL
-			&& ctx->new_table->fts->cache->sync->in_progress)) {
-			ut_a(fts_check_cached_index(ctx->new_table));
-		}
-#endif
+		ut_ad(!ctx->new_table->fts
+		      || fts_check_cached_index(ctx->new_table));
 	}
 
 	unlock_and_close_files(deleted, trx);
diff --git a/storage/innobase/include/fts0fts.h b/storage/innobase/include/fts0fts.h
index 774221dd208..043a464dd30 100644
--- a/storage/innobase/include/fts0fts.h
+++ b/storage/innobase/include/fts0fts.h
@@ -656,12 +656,6 @@ fts_optimize_remove_table(
 void
 fts_optimize_shutdown();
 
-/** Send sync fts cache for the table.
-@param[in]	table	table to sync */
-void
-fts_optimize_request_sync_table(
-	dict_table_t*	table);
-
 /**********************************************************************//**
 Take a FTS savepoint. */
 void
@@ -716,9 +710,8 @@ fts_savepoint_rollback_last_stmt(
 /** Run SYNC on the table, i.e., write out data from the cache to the
 FTS auxiliary INDEX table and clear the cache at the end.
 @param[in,out]	table		fts table
-@param[in]	wait		whether to wait for existing sync to finish
 @return DB_SUCCESS on success, error code on failure. */
-dberr_t fts_sync_table(dict_table_t* table, bool wait = true);
+dberr_t fts_sync_table(dict_table_t* table);
 
 /****************************************************************//**
 Create an FTS index cache. */
diff --git a/storage/innobase/include/fts0types.h b/storage/innobase/include/fts0types.h
index fb278d543c4..04e99d595c5 100644
--- a/storage/innobase/include/fts0types.h
+++ b/storage/innobase/include/fts0types.h
@@ -75,7 +75,6 @@ struct fts_index_cache_t {
 
 	que_t**		ins_graph;	/*!< Insert query graphs */
 
-	que_t**		sel_graph;	/*!< Select query graphs */
 	CHARSET_INFO*	charset;	/*!< charset */
 };
 
@@ -87,35 +86,7 @@ struct fts_stopword_t {
 	CHARSET_INFO*	charset;	/*!< charset for stopword */
 };
 
-/** The SYNC state of the cache. There is one instance of this struct
-associated with each ADD thread. */
-struct fts_sync_t {
-	trx_t*		trx;		/*!< The transaction used for SYNCing
-					the cache to disk */
-	dict_table_t*	table;		/*!< Table with FTS index(es) */
-	ulint		max_cache_size;	/*!< Max size in bytes of the cache */
-	ibool		cache_full;	/*!< flag, when true it indicates that
-					we need to sync the cache to disk */
-	ulint		lower_index;	/*!< the start index of the doc id
-					vector from where to start adding
-					documents to the FTS cache */
-	ulint		upper_index;	/*!< max index of the doc id vector to
-					add to the FTS cache */
-	ibool		interrupted;	/*!< TRUE if SYNC was interrupted */
-	doc_id_t	min_doc_id;	/*!< The smallest doc id added to the
-					cache. It should equal to
-					doc_ids[lower_index] */
-	doc_id_t	max_doc_id;	/*!< The doc id at which the cache was
-					noted as being full, we use this to
-					set the upper_limit field */
-	time_t		start_time;	/*!< SYNC start time; only used if
-					fts_enable_diag_print */
-	bool		in_progress;	/*!< flag whether sync is in progress.*/
-	bool		unlock_cache;	/*!< flag whether unlock cache when
-					write fts node */
-  /** condition variable for in_progress; used with table->fts->cache->lock */
-  pthread_cond_t cond;
-};
+struct fts_sync_t;
 
 /** The cache for the FTS system. It is a memory-based inverted index
 that new entries are added to, until it grows over the configured maximum
@@ -204,7 +175,6 @@ struct fts_node_t {
 	ulint		ilist_size_alloc;
 					/*!< Allocated size of ilist in
 					bytes */
-	bool		synced;		/*!< flag whether the node is synced */
 };
 
 /** A tokenizer word. Contains information about one word. */