ITS#7635 simplify 9474c1a0b6

libraries/liblmdb/mdb.c

@@ -1743,7 +1743,6 @@ mdb_txn_renew0(MDB_txn *txn)
 	unsigned int i;
 	uint16_t x;
 	int rc, new_notls = 0;
-	pgno_t lastpg2;
 
 	/* Setup db info */
 	txn->mt_numdbs = env->me_numdbs;
@@ -1790,13 +1789,11 @@ mdb_txn_renew0(MDB_txn *txn)
 			txn->mt_u.reader = r;
 		}
 		txn->mt_toggle = txn->mt_txnid & 1;
-		txn->mt_next_pgno = env->me_metas[txn->mt_toggle]->mm_last_pg+1;
 	} else {
 		LOCK_MUTEX_W(env);
 
 		txn->mt_txnid = env->me_txns->mti_txnid;
 		txn->mt_toggle = txn->mt_txnid & 1;
-		txn->mt_next_pgno = env->me_metas[txn->mt_toggle]->mm_last_pg+1;
 		txn->mt_txnid++;
 #if MDB_DEBUG
 		if (txn->mt_txnid == mdb_debug_start)
@@ -1812,17 +1809,10 @@ mdb_txn_renew0(MDB_txn *txn)
 
 	/* Copy the DB info and flags */
 	memcpy(txn->mt_dbs, env->me_metas[txn->mt_toggle]->mm_dbs, 2 * sizeof(MDB_db));
-	/* In a read txn, there is a data race here. Make sure our
-	 * last_pg/next_pg are up to date.
-	 */
-	lastpg2 = env->me_metas[txn->mt_toggle]->mm_last_pg+1;
-	if (lastpg2 != txn->mt_next_pgno) {
-		txn->mt_next_pgno = lastpg2;
-		/* When this situation occurs, the txnid will certainly also
-		 * be out of date. But as noted before, we don't care about having
-		 * up to date read txn IDs.
-		 */
-	}
+
+	/* Moved to here to avoid a data race in read TXNs */
+	txn->mt_next_pgno = env->me_metas[txn->mt_toggle]->mm_last_pg+1;
+
 	for (i=2; i<txn->mt_numdbs; i++) {
 		x = env->me_dbflags[i];
 		txn->mt_dbs[i].md_flags = x & PERSISTENT_FLAGS;