Improvement CORE-5921 : Provide information about Global Commit Number, Commit Number of currently used database snapshot (if any) and Commit Numbers assigned to the committed transactions.

doc/sql.extensions/README.builtin_functions.txt

@@ -733,6 +733,37 @@ Example:
     select * from x order by rand();
 
 
+--------------------
+RDB$GET_TRANSACTION_CN
+--------------------
+
+(FB4 extension)
+Function:
+    Returns commit number of given transaction. 
+	Note, engine internally uses unsigned 8-bit integer for commit numbers, 
+	while SQL language have no unsigned integers, thus one should be ready 
+	to see negative numbers here (it is possible only if engine commits more 
+	than 2^32 transactions since last database start, as global commit number
+	is reset at each restart).
+
+	There are some "special" values used for non-committed transactions and
+	transactions,  committed before database was started:
+
+	0 - transaction is active,
+	1 - transaction committed before database started
+	-2 - transaction is dead (rolled back)
+	-1 - transaction is in limbo
+
+	See also README.read_consistency.md
+
+Format:
+    RDB$SYSTEM_PRIVILEGE( <number> )
+
+Examples:
+	select rdb$get_transaction_cn(current_transaction) from rdb$database;
+	select rdb$get_transaction_cn(123) from rdb$database;
+
+
 --------------------
 RDB$SYSTEM_PRIVILEGE
 --------------------

doc/sql.extensions/README.context_variables2

@@ -102,6 +102,13 @@ Usage:
                     | same as of CURRENT_ROLE pseudo-variable
                     |
    ENGINE_VERSION   | Engine version number, e.g. "2.1.0" (since V2.1)
+                    |
+   GLOBAL_CN        | Most current value of global Commit Number counter
+                    |
+   SNAPSHOT_CN      | Value of Commit Number of currently database snapshot: either
+                    | transaction level (for SNAPSHOT or CONSISTENCY transaction),
+                    | or request level (for READ COMMITTED READ CONSISTENCY 
+                    | transaction). NULL, if snapshot is not exist.
 
 Notes:
    To prevent DoS attacks against Firebird Server you are not allowed to have

src/dsql/parse.y

@@ -630,6 +630,7 @@ using namespace Firebird;
 %token <metaNamePtr> VARBINARY
 %token <metaNamePtr> WINDOW
 %token <metaNamePtr> CONSISTENCY
+%token <metaNamePtr> RDB_GET_TRANSACTION_CN
 
 // external connections pool management
 %token <metaNamePtr> CONNECTIONS
@@ -7787,6 +7788,7 @@ system_function_std_syntax
 	| POWER
 	| RAND
 	| RDB_GET_CONTEXT
+	| RDB_GET_TRANSACTION_CN
 	| RDB_ROLE_IN_USE
 	| RDB_SET_CONTEXT
 	| REPLACE

src/jrd/SysFunction.cpp

@@ -46,6 +46,7 @@
 #include "../jrd/mov_proto.h"
 #include "../jrd/pag_proto.h"
 #include "../jrd/tra_proto.h"
+#include "../jrd/tpc_proto.h"
 #include "../jrd/scl_proto.h"
 #include "../common/os/guid.h"
 #include "../jrd/license.h"
@@ -169,6 +170,7 @@ void setParamsDblDec(DataTypeUtilBase* dataTypeUtil, const SysFunction* function
 void setParamsDecFloat(DataTypeUtilBase* dataTypeUtil, const SysFunction* function, int argsCount, dsc** args);
 void setParamsFromList(DataTypeUtilBase* dataTypeUtil, const SysFunction* function, int argsCount, dsc** args);
 void setParamsInteger(DataTypeUtilBase* dataTypeUtil, const SysFunction* function, int argsCount, dsc** args);
+void setParamsInt64(DataTypeUtilBase* dataTypeUtil, const SysFunction* function, int argsCount, dsc** args);
 void setParamsSecondInteger(DataTypeUtilBase* dataTypeUtil, const SysFunction* function, int argsCount, dsc** args);
 
 // specific setParams functions
@@ -235,6 +237,7 @@ dsc* evlFloor(thread_db* tdbb, const SysFunction* function, const NestValueArray
 dsc* evlGenUuid(thread_db* tdbb, const SysFunction* function, const NestValueArray& args, impure_value* impure);
 dsc* evlGetContext(thread_db* tdbb, const SysFunction* function, const NestValueArray& args, impure_value* impure);
 dsc* evlSetContext(thread_db* tdbb, const SysFunction* function, const NestValueArray& args, impure_value* impure);
+dsc* evlGetTranCN(thread_db* tdbb, const SysFunction* function, const NestValueArray& args, impure_value* impure);
 dsc* evlHash(thread_db* tdbb, const SysFunction* function, const NestValueArray& args, impure_value* impure);
 dsc* evlLeft(thread_db* tdbb, const SysFunction* function, const NestValueArray& args, impure_value* impure);
 dsc* evlLnLog10(thread_db* tdbb, const SysFunction* function, const NestValueArray& args, impure_value* impure);
@@ -276,6 +279,7 @@ const char
 	// SYSTEM namespace: global and database wise items
 	ENGINE_VERSION[] = "ENGINE_VERSION",
 	DATABASE_NAME[] = "DB_NAME",
+	GLOBAL_CN_NAME[] = "GLOBAL_CN",
 	EXT_CONN_POOL_SIZE[] = "EXT_CONN_POOL_SIZE",
 	EXT_CONN_POOL_IDLE[] = "EXT_CONN_POOL_IDLE_COUNT",
 	EXT_CONN_POOL_ACTIVE[] = "EXT_CONN_POOL_ACTIVE_COUNT",
@@ -298,6 +302,7 @@ const char
 	ISOLATION_LEVEL_NAME[] = "ISOLATION_LEVEL",
 	LOCK_TIMEOUT_NAME[] = "LOCK_TIMEOUT",
 	READ_ONLY_NAME[] = "READ_ONLY",
+	SNAPSHOT_CN_NAME[] = "SNAPSHOT_CN",
 	// DDL_TRIGGER namespace
 	DDL_EVENT_NAME[] = "DDL_EVENT",
 	EVENT_TYPE_NAME[] = "EVENT_TYPE",
@@ -473,6 +478,16 @@ void setParamsInteger(DataTypeUtilBase*, const SysFunction*, int argsCount, dsc*
 }
 
 
+void setParamsInt64(DataTypeUtilBase*, const SysFunction*, int argsCount, dsc** args)
+{
+	for (int i = 0; i < argsCount; ++i)
+	{
+		if (args[i]->isUnknown())
+			args[i]->makeInt64(0);
+	}
+}
+
+
 void setParamsSecondInteger(DataTypeUtilBase*, const SysFunction*, int argsCount, dsc** args)
 {
 	if (argsCount >= 2)
@@ -2685,6 +2700,24 @@ dsc* evlGetContext(thread_db* tdbb, const SysFunction*, const NestValueArray& ar
 			resultStr.printf("%" SLONGFORMAT, transaction->tra_lock_timeout);
 		else if (nameStr == READ_ONLY_NAME)
 			resultStr = (transaction->tra_flags & TRA_readonly) ? TRUE_VALUE : FALSE_VALUE;
+		else if (nameStr == GLOBAL_CN_NAME)
+			resultStr.printf("%" SQUADFORMAT, dbb->dbb_tip_cache->getGlobalCommitNumber());
+		else if (nameStr == SNAPSHOT_CN_NAME)
+		{
+			if (!(transaction->tra_flags & TRA_read_committed))
+				resultStr.printf("%" SQUADFORMAT, transaction->tra_snapshot_number);
+			else if ((transaction->tra_flags & TRA_read_committed) &&
+				(transaction->tra_flags & TRA_read_consistency))
+			{
+				jrd_req* snapshot_req = request->req_snapshot.m_owner;
+				if (snapshot_req)
+					resultStr.printf("%" SQUADFORMAT, snapshot_req->req_snapshot.m_number);
+				else
+					return NULL;
+			}
+			else
+				return NULL;
+		}
 		else if (nameStr == EXT_CONN_POOL_SIZE)
 			resultStr.printf("%d", EDS::Manager::getConnPool()->getMaxCount());
 		else if (nameStr == EXT_CONN_POOL_IDLE)
@@ -2890,6 +2923,38 @@ dsc* evlSetContext(thread_db* tdbb, const SysFunction*, const NestValueArray& ar
 }
 
 
+dsc* evlGetTranCN(thread_db* tdbb, const SysFunction* function, const NestValueArray& args, 
+	impure_value* impure)
+{
+	fb_assert(args.getCount() == 1);
+
+	Database* dbb = tdbb->getDatabase();
+	jrd_req* request = tdbb->getRequest();
+
+	request->req_flags &= ~req_null;
+	const dsc* value = EVL_expr(tdbb, request, args[0]);
+	if (request->req_flags & req_null)
+		return NULL;
+
+	TraNumber traNum = MOV_get_int64(tdbb, value, 0);
+	if (traNum > dbb->dbb_next_transaction)
+	{
+		request->req_flags |= req_null;
+		return NULL;
+	}
+
+	CommitNumber cn = dbb->dbb_tip_cache->snapshotState(tdbb, traNum);
+
+	dsc result;
+	result.makeInt64(0, (SINT64*)&cn);
+
+	EVL_make_value(tdbb, &result, impure);
+
+	request->req_flags &= ~req_null;
+	return &impure->vlu_desc;
+}
+
+
 dsc* evlHash(thread_db* tdbb, const SysFunction*, const NestValueArray& args,
 	impure_value* impure)
 {
@@ -4565,6 +4630,7 @@ const SysFunction SysFunction::functions[] =
 		{"QUANTIZE", 2, 2, setParamsDecFloat, makeDecFloatResult, evlQuantize, NULL},
 		{"RAND", 0, 0, NULL, makeDoubleResult, evlRand, NULL},
 		{RDB_GET_CONTEXT, 2, 2, setParamsGetSetContext, makeGetSetContext, evlGetContext, NULL},
+		{"RDB$GET_TRANSACTION_CN", 1, 1, setParamsInt64, makeInt64Result, evlGetTranCN, NULL},
 		{"RDB$ROLE_IN_USE", 1, 1, setParamsAsciiVal, makeBooleanResult, evlRoleInUse, NULL},
 		{RDB_SET_CONTEXT, 3, 3, setParamsGetSetContext, makeGetSetContext, evlSetContext, NULL},
 		{"RDB$SYSTEM_PRIVILEGE", 1, 1, NULL, makeBooleanResult, evlSystemPrivilege, NULL},

src/jrd/tpc_proto.h

@@ -140,6 +140,11 @@ public:
 	//void assignLatestTransactionId(TraNumber number);
 	void assignLatestAttachmentId(AttNumber number);
 
+	CommitNumber getGlobalCommitNumber() const
+	{
+		return m_tpcHeader->getHeader()->latest_commit_number.load(std::memory_order_acquire);
+	}
+
 private:
 	class GlobalTpcHeader : public Firebird::MemoryHeader
 	{

src/yvalve/keywords.cpp

@@ -355,6 +355,7 @@ static const TOK tokens[] =
 	{TOK_DB_KEY, "RDB$DB_KEY", false},
 	{TOK_RDB_ERROR, "RDB$ERROR", false},
 	{TOK_RDB_GET_CONTEXT, "RDB$GET_CONTEXT", false},
+	{TOK_RDB_GET_TRANSACTION_CN, "RDB$GET_TRANSACTION_CN", false},
 	{TOK_RDB_RECORD_VERSION, "RDB$RECORD_VERSION", false},
 	{TOK_RDB_ROLE_IN_USE, "RDB$ROLE_IN_USE", false},
 	{TOK_RDB_SET_CONTEXT, "RDB$SET_CONTEXT", false},