MDEV-38412 System tablespace fails to shrink due to legacy tables

mysql-test/suite/innodb/r/sys_truncate_debug.result

@@ -54,3 +54,10 @@ InnoDB	YES	Supports transactions, row-level locking, foreign keys and encryption
 SELECT NAME, FILE_SIZE FROM INFORMATION_SCHEMA.INNODB_SYS_TABLESPACES WHERE SPACE=0;
 NAME	FILE_SIZE
 innodb_system	3145728
+#
+# MDEV-38412 System tablespace fails to shrink due to legacy tables
+#
+# restart: --innodb-data-home-dir=MYSQLTEST_VARDIR/tmp/log_corruption --innodb-log-group-home-dir=MYSQLTEST_VARDIR/tmp/log_corruption --innodb_undo_directory=MYSQLTEST_VARDIR/tmp/log_corruption --debug_dbug=d,create_dummy_sys_tables
+# restart: --innodb-data-home-dir=MYSQLTEST_VARDIR/tmp/log_corruption --innodb-log-group-home-dir=MYSQLTEST_VARDIR/tmp/log_corruption --innodb_undo_directory=MYSQLTEST_VARDIR/tmp/log_corruption --innodb_data_file_path=ibdata1:10M:autoextend:autoshrink
+FOUND 2 /InnoDB: Dropping the unknown table/ in mysqld.1.err
+# restart

mysql-test/suite/innodb/t/sys_truncate_debug.test

@@ -74,3 +74,21 @@ SELECT * FROM INFORMATION_SCHEMA.ENGINES
 WHERE engine = 'innodb'
 AND support IN ('YES', 'DEFAULT', 'ENABLED');
 SELECT NAME, FILE_SIZE FROM INFORMATION_SCHEMA.INNODB_SYS_TABLESPACES WHERE SPACE=0;
+
+--echo #
+--echo # MDEV-38412 System tablespace fails to shrink due to legacy tables
+--echo #
+let bugdir= $MYSQLTEST_VARDIR/tmp/log_corruption;
+--mkdir $bugdir
+let $dirs= --innodb-data-home-dir=$bugdir --innodb-log-group-home-dir=$bugdir --innodb_undo_directory=$bugdir;
+let $restart_parameters=$dirs --debug_dbug=d,create_dummy_sys_tables;
+--source include/restart_mysqld.inc
+
+let SEARCH_FILE = $MYSQLTEST_VARDIR/log/mysqld.1.err;
+let $restart_parameters=$dirs --innodb_data_file_path=ibdata1:10M:autoextend:autoshrink;
+--source include/restart_mysqld.inc
+let SEARCH_PATTERN=InnoDB: Dropping the unknown table;
+--source include/search_pattern_in_file.inc
+let $restart_parameters=;
+--source include/restart_mysqld.inc
+rmdir $bugdir;

storage/innobase/dict/dict0crea.cc

@@ -1311,6 +1311,53 @@ dict_create_index_step(
 	return(thr);
 }
 
+#ifdef UNIV_DEBUG
+static dberr_t create_dummy_sys_tables(trx_t *trx) noexcept
+{
+  dberr_t error= que_eval_sql(nullptr, "PROCEDURE CREATE_DUMMY_1() IS\n"
+                              "BEGIN\n"
+                              "CREATE TABLE DUMMY_1(SPACE INT, NAME CHAR);\n"
+                              "CREATE UNIQUE CLUSTERED INDEX CLUST_IND"
+                              " ON DUMMY_1(SPACE);\n"
+                              "END;\n", trx);
+  if (error)
+    return error;
+
+  dict_table_t *dummy1= dict_sys.load_table("DUMMY_1");
+  if (dummy1)
+  {
+    dict_index_t *clust_idx= dummy1->indexes.start;
+    if (clust_idx && clust_idx->page != FIL_NULL)
+    {
+      mtr_t drop_mtr{trx};
+      drop_mtr.start();
+      btr_free_if_exists(fil_system.sys_space, clust_idx->page,
+                         clust_idx->page, &drop_mtr);
+      drop_mtr.commit();
+      pars_info_t *info= pars_info_create();
+      pars_info_add_ull_literal(info, "index_id", clust_idx->id);
+      pars_info_add_int4_literal(info, "page_no", FIL_NULL);
+      error= que_eval_sql(info,
+        "PROCEDURE UPDATE_DUMMY_1_PAGE() IS\n"
+        "BEGIN\n"
+        "UPDATE SYS_INDEXES SET PAGE_NO = :page_no"
+        " WHERE ID = :index_id;\n"
+        "END;\n", trx);
+      if (error)
+	return error;
+    }
+  }
+
+  return que_eval_sql(nullptr, "PROCEDURE CREATE_DUMMY_2() IS\n"
+                      "BEGIN\n"
+                      "CREATE TABLE\n"
+                      "DUMMY_2(TABLE_ID BIGINT, POS INT);\n"
+                      "CREATE UNIQUE CLUSTERED INDEX CLUST_IND"
+                      " ON DUMMY_2(TABLE_ID, POS);\n"
+                      "END;\n", trx);
+}
+#endif /* UNIV_DEBUG */
+
 bool dict_sys_t::load_sys_tables() noexcept
 {
   ut_ad(!srv_any_background_activity());
@@ -1459,6 +1506,16 @@ dberr_t dict_sys_t::create_or_check_sys_tables() noexcept
     }
   }
 
+  DBUG_EXECUTE_IF("create_dummy_sys_tables",
+                  {
+                    error= create_dummy_sys_tables(trx);
+                    if (error)
+                    {
+                      tablename = "DUMMY";
+                      goto err_exit;
+                    }
+                  });
+
   trx->commit();
   row_mysql_unlock_data_dictionary(trx);
   trx->clear_and_free();

storage/innobase/handler/ha_innodb.cc

@@ -1822,6 +1822,17 @@ static int innodb_check_version(handlerton *hton, const char *path,
     DBUG_RETURN(2);
 }
 
+static bool should_drop_garbage_table(const rec_t* rec, ulint len)
+{
+  if (len < tmp_file_prefix_length)
+    return false;
+
+  if (const char *f= static_cast<const char*>
+      (memchr(rec, '/', len - tmp_file_prefix_length)))
+    return !memcmp(f + 1, tmp_file_prefix, tmp_file_prefix_length);
+  return false;
+}
+
 /** Drop any garbage intermediate tables that existed in the system
 after a backup was restored.
 
@@ -1833,109 +1844,7 @@ data dictionary (while the data files themselves are missing).
 We will attempt to drop the tables here. */
 static void drop_garbage_tables_after_restore()
 {
-  btr_pcur_t pcur;
-  trx_t *trx= trx_create();
-  mtr_t mtr{trx};
-
-  ut_ad(!purge_sys.enabled());
-  ut_d(purge_sys.stop_FTS());
-
-  mtr.start();
-  if (pcur.open_leaf(true, dict_sys.sys_tables->indexes.start, BTR_SEARCH_LEAF,
-                     &mtr) != DB_SUCCESS)
-    goto all_fail;
-  for (;;)
-  {
-    btr_pcur_move_to_next_user_rec(&pcur, &mtr);
-
-    if (!btr_pcur_is_on_user_rec(&pcur))
-      break;
-
-    const rec_t *rec= btr_pcur_get_rec(&pcur);
-    if (rec_get_deleted_flag(rec, 0))
-      continue;
-
-    static_assert(DICT_FLD__SYS_TABLES__NAME == 0, "compatibility");
-    size_t len;
-    if (rec_get_1byte_offs_flag(rec))
-    {
-      len= rec_1_get_field_end_info(rec, 0);
-      if (len & REC_1BYTE_SQL_NULL_MASK)
-        continue; /* corrupted SYS_TABLES.NAME */
-    }
-    else
-    {
-      len= rec_2_get_field_end_info(rec, 0);
-      static_assert(REC_2BYTE_EXTERN_MASK == 16384, "compatibility");
-      if (len >= REC_2BYTE_EXTERN_MASK)
-        continue; /* corrupted SYS_TABLES.NAME */
-    }
-
-    if (len < tmp_file_prefix_length)
-      continue;
-    if (const char *f= static_cast<const char*>
-        (memchr(rec, '/', len - tmp_file_prefix_length)))
-    {
-      if (memcmp(f + 1, tmp_file_prefix, tmp_file_prefix_length))
-        continue;
-    }
-    else
-      continue;
-
-    btr_pcur_store_position(&pcur, &mtr);
-    btr_pcur_commit_specify_mtr(&pcur, &mtr);
-
-    trx_start_for_ddl(trx);
-    std::vector<pfs_os_file_t> deleted;
-    dberr_t err= DB_TABLE_NOT_FOUND;
-    row_mysql_lock_data_dictionary(trx);
-
-    if (dict_table_t *table= dict_sys.load_table
-        ({reinterpret_cast<const char*>(pcur.old_rec), len},
-         DICT_ERR_IGNORE_DROP))
-    {
-      table->acquire();
-      row_mysql_unlock_data_dictionary(trx);
-      err= lock_table_for_trx(table, trx, LOCK_X);
-      if (err == DB_SUCCESS &&
-          (table->flags2 & (DICT_TF2_FTS_HAS_DOC_ID | DICT_TF2_FTS)))
-      {
-        fts_optimize_remove_table(table);
-        err= fts_lock_tables(trx, *table);
-      }
-      if (err == DB_SUCCESS)
-        err= lock_sys_tables(trx);
-      row_mysql_lock_data_dictionary(trx);
-      table->release();
-
-      if (err == DB_SUCCESS)
-        err= trx->drop_table(*table);
-      if (err != DB_SUCCESS)
-        goto fail;
-      trx->commit(deleted);
-    }
-    else
-    {
-fail:
-      trx->rollback();
-      sql_print_error("InnoDB: cannot drop %.*s: %s",
-                      static_cast<int>(len), pcur.old_rec, ut_strerr(err));
-    }
-
-    row_mysql_unlock_data_dictionary(trx);
-    for (pfs_os_file_t d : deleted)
-      os_file_close(d);
-
-    mtr.start();
-    if (pcur.restore_position(BTR_SEARCH_LEAF, &mtr) == btr_pcur_t::CORRUPTED)
-      break;
-  }
-
-all_fail:
-  mtr.commit();
-  trx->clear_and_free();
-  ut_free(pcur.old_rec_buf);
-  ut_d(purge_sys.resume_FTS());
+  drop_tables_by_filter(should_drop_garbage_table);
 }
 
 static int innodb_ddl_recovery_done(handlerton*)

storage/innobase/include/srv0srv.h

@@ -683,3 +683,10 @@ static inline void srv_start_periodic_timer(std::unique_ptr<tpool::timer>& t,
 
 void srv_thread_pool_init();
 void srv_thread_pool_end();
+
+/** Function type for filtering tables to drop */
+using MatchFilter = bool (*)(const rec_t* rec, ulint len);
+
+/** Drop tables from SYS_TABLES matching a filter function.
+@param should_drop  function to determine if a table should be dropped*/
+void drop_tables_by_filter(MatchFilter should_drop) noexcept;