Support unique sequences through XTM

Author: knizhnik

contrib/mmts/multimaster.c

@@ -134,6 +134,7 @@ static char const* MtmGetName(void);
 static size_t MtmGetTransactionStateSize(void);
 static void MtmSerializeTransactionState(void* ctx);
 static void MtmDeserializeTransactionState(void* ctx);
+static void MtmInitializeSequence(int64* start, int64* step);
 
 static void MtmCheckClusterLock(void);
 static void MtmCheckSlots(void);
@@ -171,7 +172,8 @@ static TransactionManager MtmTM = {
 	MtmGetName,
 	MtmGetTransactionStateSize,
 	MtmSerializeTransactionState,
-	MtmDeserializeTransactionState
+	MtmDeserializeTransactionState,
+	MtmInitializeSequence
 };
 
 char const* const MtmNodeStatusMnem[] = 
@@ -349,6 +351,13 @@ MtmDeserializeTransactionState(void* ctx)
 }
 
 
+static void
+MtmInitializeSequence(int64* start, int64* step)
+{
+	*start = MtmNodeId;
+	*step = MtmMaxNodes;
+}
+
 
 /*
  * -------------------------------------------

contrib/pg_dtm/pg_dtm.c

@@ -122,7 +122,8 @@ static TransactionManager DtmTM = {
 	DtmGetName,
 	PgGetTransactionStateSize,
 	PgSerializeTransactionState,
-	PgDeserializeTransactionState	
+	PgDeserializeTransactionState,
+	PgInitializeSequence
 };
 
 static char *Arbiters;
@@ -146,6 +147,13 @@ static char const* DtmGetName(void)
 	return "pg_dtm";
 }
 
+static void
+DtmInitializeSequence(int64* init, int64* step)
+{
+	*init = MtmNodeId;
+	*step = MtmMaxNodes;
+}
+
 
 static void DumpSnapshot(Snapshot s, char *name)
 {

contrib/pg_tsdtm/pg_tsdtm.c

@@ -120,7 +120,8 @@ static TransactionManager DtmTM = {
 	DtmGetName,
 	DtmGetTransactionStateSize,
 	DtmSerializeTransactionState,
-	DtmDeserializeTransactionState
+	DtmDeserializeTransactionState,
+	PgInitializeSequence
 };
 
 void		_PG_init(void);

src/backend/access/transam/xtm.c

@@ -52,6 +52,12 @@ PgDeserializeTransactionState(void* ctx)
 {
 }
 
+void PgInitializeSequence(int64* init, int64* step)
+{
+	*init = 1;
+	*step = 1;
+}
+
 
 TransactionManager PgTM = {
 	PgTransactionIdGetStatus,
@@ -66,7 +72,8 @@ TransactionManager PgTM = {
 	PgGetTransactionManagerName,
 	PgGetTransactionStateSize,
 	PgSerializeTransactionState,
-	PgDeserializeTransactionState
+	PgDeserializeTransactionState,
+	PgInitializeSequence
 };
 
 TransactionManager *TM = &PgTM;

src/backend/commands/sequence.c

@@ -18,6 +18,7 @@
 #include "access/multixact.h"
 #include "access/transam.h"
 #include "access/xact.h"
+#include "access/xtm.h"
 #include "access/xlog.h"
 #include "access/xloginsert.h"
 #include "access/xlogutils.h"
@@ -1329,10 +1330,15 @@ init_params(List *options, bool isInit,
 		new->start_value = defGetInt64(start_value);
 	else if (isInit)
 	{
-		if (new->increment_by > 0)
-			new->start_value = new->min_value;	/* ascending seq */
-		else
-			new->start_value = new->max_value;	/* descending seq */
+		if (increment_by == NULL) { 
+            /* if neither start, neither increment are not specified explcitly, assign this values using XTM API */
+			TM->InitializeSequence(&new->start_value, &new->increment_by);
+		} else { 
+			if (new->increment_by > 0)
+				new->start_value = new->min_value;	/* ascending seq */
+			else
+				new->start_value = new->max_value;	/* descending seq */
+		}
 	}
 
 	/* crosscheck START */

src/include/access/xtm.h

@@ -88,6 +88,12 @@ typedef struct
 	 */	
 	void        (*DeserializeTransactionState)(void* ctx);
 
+	/*
+	 * Assign initial value and step to new sequence if them are not specified explicitly.
+	 * This function allows to generate unique (but not monotonic) values in distributed cluster
+	 */
+	void        (*InitializeSequence)(int64* start, int64* step);
+
 }	TransactionManager;
 
 /* Get pointer to transaction manager: actually returns content of TM variable */
@@ -121,6 +127,7 @@ extern char const *PgGetTransactionManagerName(void);
 extern size_t PgGetTransactionStateSize(void);
 extern void PgSerializeTransactionState(void* ctx);
 extern void PgDeserializeTransactionState(void* ctx);
+extern void PgInitializeSequence(int64* start, int64* step);
 
 
 #endif