Use repeatable read isolation level

knizhnik · knizhnik · commit cfe045428bd2 · 2015-09-18T20:14:54.000+03:00
diff --git a/contrib/pg_xtm/pg_dtm.c b/contrib/pg_xtm/pg_dtm.c
@@ -209,16 +209,20 @@ static void DtmUpdateRecentXmin(void)
 
 static Snapshot DtmGetSnapshot(Snapshot snapshot)
 {
-    XTM_TRACE("XTM: DtmGetSnapshot \n");
-    if (DtmGlobalTransaction/* && !DtmHasSnapshot*/) { 
-        DtmHasSnapshot = true;
-        DtmEnsureConnection();
-        DtmGlobalGetSnapshot(DtmConn, DtmNodeId, GetCurrentTransactionId(), &DtmSnapshot);
-    }
-    snapshot = GetLocalSnapshotData(snapshot);        
-    if (DtmHasSnapshot) {  
-        DtmCopySnapshot(snapshot, &DtmSnapshot);
-        DtmUpdateRecentXmin();
+    if (!IsMVCCSnapshot(snapshot) || snapshot == &CatalogSnapshotData) { 
+         snapshot = GetLocalSnapshotData(snapshot);        
+    } else { 
+        XTM_TRACE("XTM: DtmGetSnapshot \n");
+        if (DtmGlobalTransaction/* && !DtmHasSnapshot*/) { 
+            DtmHasSnapshot = true;
+            DtmEnsureConnection();
+            DtmGlobalGetSnapshot(DtmConn, DtmNodeId, GetCurrentTransactionId(), &DtmSnapshot);
+        }
+        snapshot = GetLocalSnapshotData(snapshot);        
+        if (DtmHasSnapshot) {  
+            DtmCopySnapshot(snapshot, &DtmSnapshot);
+            DtmUpdateRecentXmin();
+        }
     }
     return snapshot;
 }
diff --git a/contrib/pg_xtm/tests/transfers.go b/contrib/pg_xtm/tests/transfers.go
@@ -3,7 +3,7 @@ package main
 import (
     "fmt"
     "sync"
-    "math/rand"
+//    "math/rand"
     "github.com/jackc/pgx"
 )
 
@@ -94,6 +94,7 @@ func max(a, b int64) int64 {
 func transfer(id int, wg *sync.WaitGroup) {
     var err error
     var xids []int32 = make([]int32, 2)
+    var nConflicts = 0
 
     conn1, err := pgx.Connect(cfg1)
     checkErr(err)
@@ -106,12 +107,12 @@ func transfer(id int, wg *sync.WaitGroup) {
     for i := 0; i < N_ITERATIONS; i++ {
         //amount := 2*rand.Intn(2) - 1
         amount := 1
-        account1 := rand.Intn(N_ACCOUNTS) 
-        account2 := rand.Intn(N_ACCOUNTS)
+        account1 := id//rand.Intn(N_ACCOUNTS) 
+        account2 := id//rand.Intn(N_ACCOUNTS)
 
         // strt transaction
-        exec(conn1, "begin")
-        exec(conn2, "begin")
+        exec(conn1, "begin transaction isolation level repeatable read")
+        exec(conn2, "begin transaction isolation level repeatable read")
         
         // obtain XIDs of paticipants
         xids[0] = execQuery(conn1, "select txid_current()")
@@ -121,13 +122,17 @@ func transfer(id int, wg *sync.WaitGroup) {
         exec(conn1, "select dtm_begin_transaction($1, $2)", nodes, xids)
         exec(conn2, "select dtm_begin_transaction($1, $2)", nodes, xids)
 
-        exec(conn1, "update t set v = v + $1 where u=$2", amount, account1)
-        exec(conn2, "update t set v = v - $1 where u=$2", amount, account2)
-
-        commit(conn1, conn2)
+        if !execUpdate(conn1, "update t set v = v + $1 where u=$2", amount, account1) || 
+           !execUpdate(conn2, "update t set v = v - $1 where u=$2", amount, account2) {  
+            exec(conn1, "rollback")
+            exec(conn2, "rollback")
+            nConflicts += 1
+            i -= 1
+        } else { 
+            commit(conn1, conn2)
+        }       
     }
-
-    fmt.Println("Test completed")
+    fmt.Println("Test completed with ",nConflicts," conflicts")
     wg.Done()
 }
 
@@ -143,8 +148,8 @@ func inspect(wg *sync.WaitGroup) {
         conn2, err := pgx.Connect(cfg2)
         checkErr(err)
 
-        exec(conn1, "begin")
-        exec(conn2, "begin")
+        exec(conn1, "begin transaction isolation level repeatable read")
+        exec(conn2, "begin transaction isolation level repeatable read")
  
         // obtain XIDs of paticipants
         xids[0] = execQuery(conn1, "select txid_current()")
@@ -192,10 +197,17 @@ func main() {
 func exec(conn *pgx.Conn, stmt string, arguments ...interface{}) {
     var err error
     // fmt.Println(stmt)
-    _, _ = conn.Exec(stmt, arguments... )
+    _, err = conn.Exec(stmt, arguments... )
     checkErr(err)
 }
 
+func execUpdate(conn *pgx.Conn, stmt string, arguments ...interface{}) bool {
+    var err error
+    // fmt.Println(stmt)
+    _, err = conn.Exec(stmt, arguments... )
+    return err == nil
+}
+
 func execQuery(conn *pgx.Conn, stmt string, arguments ...interface{}) int32 {
     var err error
     var result int64
