Revert "Optimize get_global_xmin"

kelvich · kelvich · commit 21ffe4a0a15d · 2015-10-15T14:18:39.000+03:00
This reverts commit 504c5da.
diff --git a/contrib/pg_dtm/dtmd/include/transaction.h b/contrib/pg_dtm/dtmd/include/transaction.h
@@ -20,7 +20,6 @@ typedef struct L2List
 typedef struct Transaction {
     L2List elem;
 	xid_t xid;
-    xid_t xmin;
 
 	int size; // number of paritcipants
 
diff --git a/contrib/pg_dtm/dtmd/src/main.c b/contrib/pg_dtm/dtmd/src/main.c
@@ -246,13 +246,19 @@ static void onreserve(client_t client, int argc, xid_t *argv) {
 }
 
 static xid_t get_global_xmin() {
+	int j;
 	xid_t xmin = next_gxid;
 	Transaction *t;
     for (t = (Transaction*)active_transactions.next; t != (Transaction*)&active_transactions; t = (Transaction*)t->elem.next) {
-        if (t->xmin < xmin) { 
-            xmin = t->xmin;
-        }
-    }
+		j = t->snapshots_count > MAX_SNAPSHOTS_PER_TRANS ? MAX_SNAPSHOTS_PER_TRANS : t->snapshots_count; 
+		while (--j >= 0) { 
+			Snapshot* s = transaction_snapshot(t, j);
+			if (s->xmin < xmin) {
+				xmin = s->xmin;
+			}
+			// minor TODO: Use 'times_sent' to generate a bit greater xmin?
+		}
+	}
 	return xmin;
 }
 
@@ -277,6 +283,7 @@ static void onbegin(client_t client, int argc, xid_t *argv) {
         free_transactions = t->elem.next;
     }
     transaction_clear(t);
+    l2_list_link(&active_transactions, &t->elem);
 
 	prev_gxid = t->xid = next_gxid++;
 	t->snapshots_count = 0;
@@ -292,15 +299,15 @@ static void onbegin(client_t client, int argc, xid_t *argv) {
 			CLIENT_ID(client), t->xid
 		);
 		client_message_shortcut(client, RES_FAILED);
-        free_transaction(t);
 		return;
 	}
+
 	xid_t gxmin = get_global_xmin();
-	Snapshot *snap = transaction_next_snapshot(t);
-	gen_snapshot(snap); 	// FIXME: increase 'times_sent' here? see also 4765234987
 
-    t->xmin = snap->xmin;
-    l2_list_link(&active_transactions, &t->elem);
+	gen_snapshot(transaction_next_snapshot(t));
+	// will wrap around if exceeded max snapshots
+	Snapshot *snap = transaction_latest_snapshot(t);
+	// FIXME: increase 'times_sent' here? see also 4765234987
 
 	xid_t ok = RES_OK;
 	client_message_start(client); {
@@ -455,11 +462,7 @@ static void onsnapshot(client_t client, int argc, xid_t *argv) {
 
 	if (CLIENT_SNAPSENT(client) == t->snapshots_count) {
 		// a fresh snapshot is needed
-        Snapshot* snap = transaction_next_snapshot(t);
-		gen_snapshot(snap);
-        if (snap->xmin < t->xmin) { 
-            t->xmin = snap->xmin;
-        }
+		gen_snapshot(transaction_next_snapshot(t));
 	}
 
 	xid_t gxmin = get_global_xmin();
diff --git a/contrib/pg_dtm/dtmd/src/transaction.c b/contrib/pg_dtm/dtmd/src/transaction.c
@@ -27,7 +27,6 @@ void transaction_clear(Transaction *t) {
 	int i;
     
 	t->xid = INVALID_XID;
-	t->xmin = INVALID_XID;
 	t->size = 0;
 	t->votes_for = 0;
 	t->votes_against = 0;
