MDEV-32103 InnoDB ALTER TABLE is not crash-safe

Starting with commit 4ff5311
log_write_up_to(trx->commit_lsn, true) in DDL operations could end up
being a no-op, because trx->commit_lsn would be 0.

trx_flush_log_if_needed(): Revert an incorrect attempt to ensure
that DDL operations are crash-safe.

trx_t::commit(std::vector<pfs_os_file_t> &), ha_innobase::rename_table():
Set trx_t::flush_log_later so that trx_t::commit_in_memory() will
retain trx_t::commit_lsn for the final durability call.

Tested by: Matthias Leich

Author: dr-m

storage/innobase/dict/drop.cc

@@ -235,7 +235,9 @@ dberr_t trx_t::drop_table(const dict_table_t &table)
 void trx_t::commit(std::vector<pfs_os_file_t> &deleted)
 {
   ut_ad(dict_operation);
+  flush_log_later= true;
   commit_persist();
+  flush_log_later= false;
   if (dict_operation)
   {
     std::vector<uint32_t> space_ids;

storage/innobase/handler/ha_innodb.cc

@@ -14263,6 +14263,7 @@ ha_innobase::rename_table(
 	}
 
 	if (error == DB_SUCCESS) {
+		trx->flush_log_later = true;
 		innobase_commit_low(trx);
 	} else {
 		trx->rollback();
@@ -14278,6 +14279,7 @@ ha_innobase::rename_table(
 	if (error == DB_SUCCESS) {
 		log_write_up_to(trx->commit_lsn, true);
 	}
+	trx->flush_log_later = false;
 	trx->free();
 
 	if (error == DB_DUPLICATE_KEY) {

storage/innobase/trx/trx0trx.cc

@@ -1236,7 +1236,7 @@ static void trx_flush_log_if_needed(lsn_t lsn, trx_t *trx)
   if (log_sys.get_flushed_lsn() > lsn)
     return;
 
-  const bool flush= trx->dict_operation ||
+  const bool flush=
     (srv_file_flush_method != SRV_NOSYNC &&
      (srv_flush_log_at_trx_commit & 1));