Make it possible to start multiple transactions using the same initial transaction snapshot - CORE-6018 (#193)

With this feature it's possible to create parallel (via different attachments) processes reading consistent data from a database.

For example, a backup process may create multiple threads paralleling read data from the database.

Also a web service may dispatch distributed sub services paralleling doing some processing.

That is accomplished creating a transaction with SET TRANSACTION SNAPSHOT [ AT NUMBER <snapshot number> ] or isc_tpb_at_snapshot_number.

The <snapshot number> from the first transaction may be obtained with RDB$GET_CONTEXT('SYSTEM', 'SNAPSHOT_NUMBER') or transaction info call with fb_info_tra_snapshot_number.

Also added CORE-6017 - Add transaction info fb_info_tra_snapshot_number.

doc/README.transaction_at_snapshot.md

@@ -0,0 +1,17 @@
+# Transaction at defined snapshot number
+
+With this feature it's possible to create parallel (via different attachments) processes reading consistent data from a database.
+
+For example, a backup process may create multiple threads paralleling reading data from the database.
+
+Or a web service may dispatch distributed sub services paralleling doing some processing.
+
+That is accomplished creating a transaction with `SET TRANSACTION SNAPSHOT [ AT NUMBER <snapshot number> ]` or `isc_tpb_at_snapshot_number <snapshot number length> <snapshot number>`.
+
+The `snapshot number` from the first transaction may be obtained with `RDB$GET_CONTEXT('SYSTEM', 'SNAPSHOT_NUMBER')` or transaction info call with `fb_info_tra_snapshot_number`.
+
+Note that the `snapshot number` passed to the new transaction must be a snapshot of an active transaction.
+
+
+Author:
+    Adriano dos Santos Fernandes <adrianosf at gmail.com>

doc/sql.extensions/README.keywords

@@ -330,6 +330,7 @@ Firebird 4.0
     NATIVE *
     NORMALIZE_DECFLOAT *
     NTILE (1)
+    NUMBER
     OTHERS
     OVERRIDING
     PERCENT_RANK (1)

lang_helpers/gds_codes.ftn

@@ -1914,6 +1914,8 @@ C --
       PARAMETER (GDS__tom_chacha_key                   = 335545250)
       INTEGER*4 GDS__bad_repl_handle                 
       PARAMETER (GDS__bad_repl_handle                  = 335545251)
+      INTEGER*4 GDS__tra_snapshot_does_not_exist     
+      PARAMETER (GDS__tra_snapshot_does_not_exist      = 335545252)
       INTEGER*4 GDS__gfix_db_name                    
       PARAMETER (GDS__gfix_db_name                     = 335740929)
       INTEGER*4 GDS__gfix_invalid_sw                 

lang_helpers/gds_codes.pas

@@ -1909,6 +1909,8 @@ const
 	gds_tom_chacha_key                   = 335545250;
 	isc_bad_repl_handle                  = 335545251;
 	gds_bad_repl_handle                  = 335545251;
+	isc_tra_snapshot_does_not_exist      = 335545252;
+	gds_tra_snapshot_does_not_exist      = 335545252;
 	isc_gfix_db_name                     = 335740929;
 	gds_gfix_db_name                     = 335740929;
 	isc_gfix_invalid_sw                  = 335740930;

src/common/classes/BlrWriter.h

@@ -64,6 +64,12 @@ public:
 		appendUShort(val >> 16);
 	}
 
+	void appendUInt64(FB_UINT64 val)
+	{
+		appendULong(val);
+		appendULong(val >> 32);
+	}
+
 	void appendUCharRepeated(UCHAR byte, int count)
 	{
 		for (int i = 0; i < count; ++i)

src/dsql/Parser.cpp

@@ -600,7 +600,7 @@ int Parser::yylexAux()
 	 *
 	 * This code recognizes the following token types:
 	 *
-	 * NUMBER: string of digits which fits into a 32-bit integer
+	 * NUMBER32BIT: string of digits which fits into a 32-bit integer
 	 *
 	 * NUMBER64BIT: string of digits whose value might fit into an SINT64,
 	 *   depending on whether or not there is a preceding '-', which is to
@@ -792,7 +792,7 @@ int Parser::yylexAux()
 	// by a set of nibbles, using 0-9, a-f, or A-F.  Odd numbers
 	// of nibbles assume a leading '0'.  The result is converted
 	// to an integer, and the result returned to the caller.  The
-	// token is identified as a NUMBER if it's a 32-bit or less
+	// token is identified as a NUMBER32BIT if it's a 32-bit or less
 	// value, or a NUMBER64INT if it requires a 64-bit number.
 	if (c == '0' && lex.ptr + 1 < lex.end && (*lex.ptr == 'x' || *lex.ptr == 'X') &&
 		(classes(lex.ptr[1]) & CHR_HEX))
@@ -833,7 +833,7 @@ int Parser::yylexAux()
 		}
 
 		// we have a valid hex token. Now give it back, either as
-		// an NUMBER or NUMBER64BIT.
+		// an NUMBER32BIT or NUMBER64BIT.
 		if (!hexerror)
 		{
 			// if charlen > 8 (something like FFFF FFFF 0, w/o the spaces)
@@ -888,7 +888,7 @@ int Parser::yylexAux()
 			}
 			else
 			{
-				// we have an integer value. we'll return NUMBER.
+				// we have an integer value. we'll return NUMBER32BIT.
 				// but we have to make a number value to be compatible
 				// with existing code.
 
@@ -933,7 +933,7 @@ int Parser::yylexAux()
 				}
 
 				yylval.int32Val = (SLONG) value;
-				return TOK_NUMBER;
+				return TOK_NUMBER32BIT;
 			} // integer value
 		}  // if (!hexerror)...
 
@@ -1111,7 +1111,7 @@ int Parser::yylexAux()
 				{
 					yylval.int32Val = (SLONG) number;
 					//printf ("parse.y %p %d\n", yylval.legacyStr, number);
-					return TOK_NUMBER;
+					return TOK_NUMBER32BIT;
 				}
 				else
 				{

src/dsql/StmtNodes.cpp

@@ -8191,6 +8191,14 @@ SetTransactionNode* SetTransactionNode::dsqlPass(DsqlCompilerScratch* dsqlScratc
 	for (RestrictionOption** i = reserveList.begin(); i != reserveList.end(); ++i)
 		genTableLock(dsqlScratch, **i, lockLevel);
 
+	if (atSnapshotNumber.specified)
+	{
+		dsqlScratch->appendUChar(isc_tpb_at_snapshot_number);
+		static_assert(sizeof(CommitNumber) == sizeof(FB_UINT64), "sizeof(CommitNumber) == sizeof(FB_UINT64)");
+		dsqlScratch->appendUChar(sizeof(CommitNumber));
+		dsqlScratch->appendUInt64(atSnapshotNumber.value);
+	}
+
 	if (dsqlScratch->getBlrData().getCount() > 1)	// 1 -> isc_tpb_version1
 		tpb.add(dsqlScratch->getBlrData().begin(), dsqlScratch->getBlrData().getCount());
 

src/dsql/StmtNodes.h

@@ -1619,6 +1619,7 @@ public:
 	Nullable<USHORT> lockTimeout;
 	Firebird::Array<RestrictionOption*> reserveList;
 	Firebird::UCharBuffer tpb;
+	Nullable<CommitNumber> atSnapshotNumber;
 };
 
 

src/dsql/parse-conflicts.txt

@@ -1 +1 @@
-56 shift/reduce conflicts, 17 reduce/reduce conflicts.
+58 shift/reduce conflicts, 17 reduce/reduce conflicts.

src/dsql/parse.y

@@ -335,7 +335,7 @@ using namespace Firebird;
 %token <stringPtr> FLOAT_NUMBER DECIMAL_NUMBER LIMIT64_INT
 %token <lim64ptr> LIMIT64_NUMBER
 %token <metaNamePtr> SYMBOL
-%token <int32Val> NUMBER
+%token <int32Val> NUMBER32BIT
 
 %token <intlStringPtr> STRING
 %token <metaNamePtr> INTRODUCER
@@ -5358,7 +5358,7 @@ tran_option($setTransactionNode)
 	| NO WAIT
 		{ setClause($setTransactionNode->wait, "[NO] WAIT", false); }
 	// isolation mode
-	| isolation_mode
+	| isolation_mode($setTransactionNode)
 		{ setClause($setTransactionNode->isoLevel, "ISOLATION LEVEL", $1); }
 	// misc options
 	| NO AUTO UNDO
@@ -5378,24 +5378,38 @@ tran_option($setTransactionNode)
 		restr_list($setTransactionNode)
 	;
 
-%type <uintVal>	isolation_mode
-isolation_mode
-	: ISOLATION LEVEL iso_mode	{ $$ = $3;}
+%type <uintVal>	isolation_mode(<setTransactionNode>)
+isolation_mode($setTransactionNode)
+	: ISOLATION LEVEL iso_mode($setTransactionNode)	{ $$ = $3;}
 	| iso_mode
 	;
 
-%type <uintVal>	iso_mode
-iso_mode
-	: snap_shot
+%type <uintVal>	iso_mode(<setTransactionNode>)
+iso_mode($setTransactionNode)
+	: snap_shot($setTransactionNode)	{ $$ = $1; }
 	| READ UNCOMMITTED version_mode		{ $$ = $3; }
 	| READ COMMITTED version_mode		{ $$ = $3; }
 	;
 
-%type <uintVal>	snap_shot
-snap_shot
-	: SNAPSHOT					{ $$ = SetTransactionNode::ISO_LEVEL_CONCURRENCY; }
-	| SNAPSHOT TABLE			{ $$ = SetTransactionNode::ISO_LEVEL_CONSISTENCY; }
-	| SNAPSHOT TABLE STABILITY	{ $$ = SetTransactionNode::ISO_LEVEL_CONSISTENCY; }
+%type <uintVal>	snap_shot(<setTransactionNode>)
+snap_shot($setTransactionNode)
+	: SNAPSHOT
+		{ $$ = SetTransactionNode::ISO_LEVEL_CONCURRENCY; }
+	| SNAPSHOT AT NUMBER snapshot_number
+		{
+			setClause($setTransactionNode->atSnapshotNumber, "SNAPSHOT AT NUMBER", (CommitNumber) $4);
+			$$ = SetTransactionNode::ISO_LEVEL_CONCURRENCY;
+		}
+	| SNAPSHOT TABLE
+		{ $$ = SetTransactionNode::ISO_LEVEL_CONSISTENCY; }
+	| SNAPSHOT TABLE STABILITY
+		{ $$ = SetTransactionNode::ISO_LEVEL_CONSISTENCY; }
+	;
+
+%type <int64Val> snapshot_number
+snapshot_number
+	: NUMBER32BIT	{ $$ = $1; }
+	| NUMBER64BIT	{ $$ = $1.number; }
 	;
 
 %type <uintVal>	version_mode
@@ -7371,7 +7385,7 @@ u_numeric_constant
 
 %type <valueExprNode> ul_numeric_constant
 ul_numeric_constant
-	: NUMBER
+	: NUMBER32BIT
 		{ $$ = MAKE_const_slong($1); }
 	| FLOAT_NUMBER
 		{ $$ = MAKE_constant($1->c_str(), CONSTANT_DOUBLE); }
@@ -7511,7 +7525,7 @@ signed_short_integer
 
 %type <int32Val> nonneg_short_integer
 nonneg_short_integer
-	: NUMBER
+	: NUMBER32BIT
 		{
 			if ($1 > SHRT_POS_MAX)
 				yyabandon(YYPOSNARG(1), -842, isc_expec_short);	// Short integer expected
@@ -7522,7 +7536,7 @@ nonneg_short_integer
 
 %type <int32Val> neg_short_integer
 neg_short_integer
-	: NUMBER
+	: NUMBER32BIT
 		{
 			if ($1 > SHRT_NEG_MAX)
 				yyabandon(YYPOSNARG(1), -842, isc_expec_short);	// Short integer expected
@@ -7544,7 +7558,7 @@ pos_short_integer
 
 %type <int32Val> unsigned_short_integer
 unsigned_short_integer
-	: NUMBER
+	: NUMBER32BIT
 		{
 			if ($1 > SHRT_UNSIGNED_MAX)
 				yyabandon(YYPOSNARG(1), -842, isc_expec_ushort);	// Unsigned short integer expected
@@ -7561,7 +7575,7 @@ signed_long_integer
 
 %type <int32Val> long_integer
 long_integer
-	: NUMBER	{ $$ = $1;}
+	: NUMBER32BIT	{ $$ = $1;}
 	;
 
 
@@ -8796,6 +8810,7 @@ non_reserved_word
 	| NATIVE
 	| NORMALIZE_DECFLOAT
 	| NTILE
+	| NUMBER
 	| OLDEST
 	| OTHERS
 	| OVERRIDING

src/include/consts_pub.h

@@ -244,6 +244,7 @@
 #define isc_tpb_no_auto_undo              20
 #define isc_tpb_lock_timeout              21
 #define isc_tpb_read_consistency          22
+#define isc_tpb_at_snapshot_number        23
 
 
 /************************/

src/include/gen/codetext.h

@@ -953,6 +953,7 @@ static const struct {
 	{"tom_rsa_verify", 335545249},
 	{"tom_chacha_key", 335545250},
 	{"bad_repl_handle", 335545251},
+	{"tra_snapshot_does_not_exist", 335545252},
 	{"gfix_db_name", 335740929},
 	{"gfix_invalid_sw", 335740930},
 	{"gfix_incmp_sw", 335740932},

src/include/gen/iberror.h

@@ -987,6 +987,7 @@ const ISC_STATUS isc_tom_rsa_sign                     = 335545248L;
 const ISC_STATUS isc_tom_rsa_verify                   = 335545249L;
 const ISC_STATUS isc_tom_chacha_key                   = 335545250L;
 const ISC_STATUS isc_bad_repl_handle                  = 335545251L;
+const ISC_STATUS isc_tra_snapshot_does_not_exist      = 335545252L;
 const ISC_STATUS isc_gfix_db_name                     = 335740929L;
 const ISC_STATUS isc_gfix_invalid_sw                  = 335740930L;
 const ISC_STATUS isc_gfix_incmp_sw                    = 335740932L;
@@ -1461,7 +1462,7 @@ const ISC_STATUS isc_trace_switch_user_only           = 337182757L;
 const ISC_STATUS isc_trace_switch_param_miss          = 337182758L;
 const ISC_STATUS isc_trace_param_act_notcompat        = 337182759L;
 const ISC_STATUS isc_trace_mandatory_switch_miss      = 337182760L;
-const ISC_STATUS isc_err_max                          = 1405;
+const ISC_STATUS isc_err_max                          = 1406;
 
 #else /* c definitions */
 
@@ -2418,6 +2419,7 @@ const ISC_STATUS isc_err_max                          = 1405;
 #define isc_tom_rsa_verify                   335545249L
 #define isc_tom_chacha_key                   335545250L
 #define isc_bad_repl_handle                  335545251L
+#define isc_tra_snapshot_does_not_exist      335545252L
 #define isc_gfix_db_name                     335740929L
 #define isc_gfix_invalid_sw                  335740930L
 #define isc_gfix_incmp_sw                    335740932L
@@ -2892,7 +2894,7 @@ const ISC_STATUS isc_err_max                          = 1405;
 #define isc_trace_switch_param_miss          337182758L
 #define isc_trace_param_act_notcompat        337182759L
 #define isc_trace_mandatory_switch_miss      337182760L
-#define isc_err_max                          1405
+#define isc_err_max                          1406
 
 #endif
 

src/include/gen/msgs.h

@@ -956,6 +956,7 @@ Data source : @4"},		/* eds_statement */
 	{335545249, "Verifying RSA-signed data"},		/* tom_rsa_verify */
 	{335545250, "Invalid key length @1, need 16 or 32"},		/* tom_chacha_key */
 	{335545251, "invalid replicator handle"},		/* bad_repl_handle */
+	{335545252, "Transaction's base snapshot number does not exist"},		/* tra_snapshot_does_not_exist */
 	{335740929, "data base file name (@1) already given"},		/* gfix_db_name */
 	{335740930, "invalid switch @1"},		/* gfix_invalid_sw */
 	{335740932, "incompatible switch combination"},		/* gfix_incmp_sw */

src/include/gen/sql_code.h

@@ -952,6 +952,7 @@ static const struct {
 	{335545249, -901}, /* 929 tom_rsa_verify */
 	{335545250, -901}, /* 930 tom_chacha_key */
 	{335545251, -901}, /* 931 bad_repl_handle */
+	{335545252, -901}, /* 932 tra_snapshot_does_not_exist */
 	{335740929, -901}, /*   1 gfix_db_name */
 	{335740930, -901}, /*   2 gfix_invalid_sw */
 	{335740932, -901}, /*   4 gfix_incmp_sw */

src/include/gen/sql_state.h

@@ -952,6 +952,7 @@ static const struct {
 	{335545249, "22023"}, // 929 tom_rsa_verify
 	{335545250, "22023"}, // 930 tom_chacha_key
 	{335545251, "08003"}, // 931 bad_repl_handle
+	{335545252, "0B000"}, // 932 tra_snapshot_does_not_exist
 	{335740929, "00000"}, //   1 gfix_db_name
 	{335740930, "00000"}, //   2 gfix_invalid_sw
 	{335740932, "00000"}, //   4 gfix_incmp_sw

src/jrd/inf.cpp

@@ -1166,6 +1166,10 @@ void INF_transaction_info(const jrd_tra* transaction,
 			memcpy(buffer, transaction->tra_attachment->att_database->dbb_database_name.c_str(), length);
 			break;
 
+		case fb_info_tra_snapshot_number:
+			length = INF_convert(static_cast<SINT64>(transaction->tra_snapshot_number), buffer);
+			break;
+
 		default:
 			buffer[0] = item;
 			item = isc_info_error;

src/jrd/inf_pub.h

@@ -394,6 +394,7 @@ enum info_db_provider
 #define isc_info_tra_access					9
 #define isc_info_tra_lock_timeout			10
 #define fb_info_tra_dbpath					11
+#define fb_info_tra_snapshot_number			12
 
 // isc_info_tra_isolation responses
 #define isc_info_tra_consistency		1

src/jrd/tpc.cpp

@@ -759,8 +759,7 @@ void TipCache::remapSnapshots(bool sync)
 }
 
 
-
-SnapshotHandle TipCache::beginSnapshot(thread_db* tdbb, AttNumber attachmentId, CommitNumber *commitNumber_out)
+SnapshotHandle TipCache::beginSnapshot(thread_db* tdbb, AttNumber attachmentId, CommitNumber& commitNumber)
 {
 	// Can only be called on initialized TipCache
 	fb_assert(m_tpcHeader);
@@ -772,16 +771,38 @@ SnapshotHandle TipCache::beginSnapshot(thread_db* tdbb, AttNumber attachmentId,
 	// Remap snapshot list if it has been grown by someone else
 	remapSnapshots(false);
 
+	if (commitNumber != 0)
+	{
+		SnapshotList* snapshots = m_snapshots->getHeader();
+		ULONG slotsUsed = snapshots->slots_used.load(std::memory_order_relaxed);
+		bool found = false;
+
+		for (SnapshotHandle slotNumber = 0; slotNumber < slotsUsed; ++slotNumber)
+		{
+			if (snapshots->slots[slotNumber].attachment_id.load(std::memory_order_relaxed) != 0 &&
+				snapshots->slots[slotNumber].snapshot.load(std::memory_order_relaxed) == commitNumber)
+			{
+				found = true;
+				break;
+			}
+		}
+
+		if (!found)
+			ERR_post(Arg::Gds(isc_tra_snapshot_does_not_exist));
+	}
+
 	SnapshotHandle slotNumber = allocateSnapshotSlot();
 
 	// Note, that allocateSnapshotSlot might remap memory and thus invalidate pointers
 	SnapshotList* snapshots = m_snapshots->getHeader();
 
 	// Store snapshot commit number and return handle
-	SnapshotData *slot = snapshots->slots + slotNumber;
+	SnapshotData* slot = snapshots->slots + slotNumber;
 
-	*commitNumber_out = m_tpcHeader->getHeader()->latest_commit_number.load(std::memory_order_acquire);
-	slot->snapshot.store(*commitNumber_out, std::memory_order_release);
+	if (commitNumber == 0)
+		commitNumber = m_tpcHeader->getHeader()->latest_commit_number.load(std::memory_order_acquire);
+
+	slot->snapshot.store(commitNumber, std::memory_order_release);
 
 	// Only assign attachment_id after we completed all other work
 	slot->attachment_id.store(attachmentId, std::memory_order_release);

src/jrd/tpc_proto.h

@@ -118,9 +118,9 @@ public:
 	void updateOldestTransaction(thread_db* tdbb, TraNumber oldest, TraNumber oldestSnapshot);
 
 	// Create snapshot. The snapshot shall use only versions committed
-	// before commitNumber_out. Snapshots inhibit GC to some extent.
+	// before commitNumber (the latest CN when it's 0). Snapshots inhibit GC to some extent.
 	// When snapshot is no longer needed you call endSnapshot.
-	SnapshotHandle beginSnapshot(thread_db* tdbb, AttNumber attachmentId, CommitNumber *commitNumber_out);
+	SnapshotHandle beginSnapshot(thread_db* tdbb, AttNumber attachmentId, CommitNumber& commitNumber);
 
 	// Deallocate snapshot.
 	void endSnapshot(thread_db* tdbb, SnapshotHandle handle, AttNumber attachmentId);

src/jrd/tra.cpp

@@ -171,10 +171,11 @@ void TRA_setup_request_snapshot(Jrd::thread_db* tdbb, Jrd::jrd_req* request, boo
 	// we need to set up statement snapshot for read consistency and own it
 
 	request->req_snapshot.m_owner = request;
+	request->req_snapshot.m_number = 0;
 
 	request->req_snapshot.m_handle =
 		tdbb->getDatabase()->dbb_tip_cache->beginSnapshot(tdbb,
-			tdbb->getAttachment()->att_attachment_id, &request->req_snapshot.m_number);
+			tdbb->getAttachment()->att_attachment_id, request->req_snapshot.m_number);
 }
 
 
@@ -1283,8 +1284,10 @@ void TRA_release_transaction(thread_db* tdbb, jrd_tra* transaction, Jrd::TraceTr
 	}
 
 	++transaction->tra_use_count;
+
 	if (transaction->tra_lock)
 		LCK_release(tdbb, transaction->tra_lock);
+
 	--transaction->tra_use_count;
 
 	// release the sparse bit map used for commit retain transaction
@@ -2732,6 +2735,7 @@ static void transaction_options(thread_db* tdbb,
 	TriState wait, lock_timeout;
 	TriState isolation, read_only, rec_version, read_consistency;
 	bool anylock_write = false;
+	bool shared_snapshot = false;
 
 	++tpb;
 
@@ -2745,6 +2749,14 @@ static void transaction_options(thread_db* tdbb,
 				ERR_post(Arg::Gds(isc_bad_tpb_content) <<
 						 Arg::Gds(isc_tpb_multiple_txn_isolation));
 
+			if (shared_snapshot)
+			{
+				ERR_post(
+					Arg::Gds(isc_bad_tpb_content) <<
+					Arg::Gds(isc_tpb_conflicting_options) <<
+						Arg::Str("isc_tpb_consistency") << Arg::Str("isc_tpb_at_snapshot_number"));
+			}
+
 			transaction->tra_flags |= TRA_degree3;
 			transaction->tra_flags &= ~TRA_read_committed;
 			break;
@@ -2763,6 +2775,14 @@ static void transaction_options(thread_db* tdbb,
 				ERR_post(Arg::Gds(isc_bad_tpb_content) <<
 						 Arg::Gds(isc_tpb_multiple_txn_isolation));
 
+			if (shared_snapshot)
+			{
+				ERR_post(
+					Arg::Gds(isc_bad_tpb_content) <<
+					Arg::Gds(isc_tpb_conflicting_options) <<
+						Arg::Str("isc_tpb_read_committed") << Arg::Str("isc_tpb_at_snapshot_number"));
+			}
+
 			transaction->tra_flags &= ~TRA_degree3;
 			transaction->tra_flags |= TRA_read_committed;
 			break;
@@ -3143,6 +3163,70 @@ static void transaction_options(thread_db* tdbb,
 			}
 			break;
 
+		case isc_tpb_at_snapshot_number:
+			{
+				const char* option_name = "isc_tpb_at_snapshot_number";
+
+				if (shared_snapshot)
+				{
+					ERR_post(
+						Arg::Gds(isc_bad_tpb_content) <<
+						Arg::Gds(isc_tpb_multiple_spec) << Arg::Str(option_name));
+				}
+
+				if (transaction->tra_flags & TRA_read_committed)
+				{
+					ERR_post(
+						Arg::Gds(isc_bad_tpb_content) <<
+						Arg::Gds(isc_tpb_conflicting_options) <<
+							Arg::Str(option_name) << Arg::Str("isc_tpb_read_committed"));
+				}
+
+				if (transaction->tra_flags & TRA_degree3)
+				{
+					ERR_post(
+						Arg::Gds(isc_bad_tpb_content) <<
+						Arg::Gds(isc_tpb_conflicting_options) <<
+							Arg::Str(option_name) << Arg::Str("isc_tpb_consistency"));
+				}
+
+				if (tpb >= end)
+				{
+					ERR_post(
+						Arg::Gds(isc_bad_tpb_content) <<
+						Arg::Gds(isc_tpb_missing_len) << Arg::Str(option_name));
+				}
+
+				const USHORT len = *tpb++;
+
+				if (tpb >= end && len > 0)
+				{
+					ERR_post(
+						Arg::Gds(isc_bad_tpb_content) <<
+						Arg::Gds(isc_tpb_missing_value) << Arg::Num(len) << Arg::Str(option_name));
+				}
+
+				if (end - tpb < len || len == 0)
+				{
+					ERR_post(
+						Arg::Gds(isc_bad_tpb_content) <<
+						Arg::Gds(isc_tpb_corrupt_len) << Arg::Num(len) << Arg::Str(option_name));
+				}
+
+				shared_snapshot = true;
+				transaction->tra_snapshot_number = isc_portable_integer(tpb, len);
+
+				if (transaction->tra_snapshot_number == 0)
+				{
+					ERR_post(
+						Arg::Gds(isc_bad_tpb_content) <<
+						Arg::Str(option_name));
+				}
+
+				tpb += len;
+			}
+			break;
+
 		default:
 			ERR_post(Arg::Gds(isc_bad_tpb_form));
 		}
@@ -3326,9 +3410,16 @@ static void transaction_start(thread_db* tdbb, jrd_tra* trans)
 
 		if (!(trans->tra_flags & TRA_read_committed))
 		{
-			trans->tra_snapshot_handle =
-				dbb->dbb_tip_cache->beginSnapshot(tdbb,
-					attachment->att_attachment_id, &trans->tra_snapshot_number);
+			try
+			{
+				trans->tra_snapshot_handle = dbb->dbb_tip_cache->beginSnapshot(
+					tdbb, attachment->att_attachment_id, trans->tra_snapshot_number);
+			}
+			catch (const Firebird::Exception&)
+			{
+				LCK_release(tdbb, lock);
+				throw;
+			}
 		}
 
 		// Next task is to find the oldest active transaction on the system.  This

src/msgs/facilities2.sql

@@ -1,7 +1,7 @@
 /* MAX_NUMBER is the next number to be used, always one more than the highest message number. */
 set bulk_insert INSERT INTO FACILITIES (LAST_CHANGE, FACILITY, FAC_CODE, MAX_NUMBER) VALUES (?, ?, ?, ?);
 --
-('2019-01-14 20:23:00', 'JRD', 0, 932)
+('2019-03-01 12:35:00', 'JRD', 0, 933)
 ('2015-03-17 18:33:00', 'QLI', 1, 533)
 ('2018-03-17 12:00:00', 'GFIX', 3, 136)
 ('1996-11-07 13:39:40', 'GPRE', 4, 1)

src/msgs/messages2.sql

@@ -1039,6 +1039,7 @@ Data source : @4', NULL, NULL)
 ('tom_rsa_verify', NULL, 'SysFunction.cpp', NULL, 0, 929, NULL, 'Verifying RSA-signed data', NULL, NULL);
 ('tom_chacha_key', NULL, 'SysFunction.cpp', NULL, 0, 930, NULL, 'Invalid key length @1, need 16 or 32', NULL, NULL);
 ('bad_repl_handle', NULL, 'jrd.cpp', NULL, 0, 931, NULL, 'invalid replicator handle', NULL, NULL);
+('tra_snapshot_does_not_exist', NULL, 'tpc.cpp', NULL, 0, 932, NULL, 'Transaction''s base snapshot number does not exist', NULL, NULL);
 -- QLI
 (NULL, NULL, NULL, NULL, 1, 0, NULL, 'expected type', NULL, NULL);
 (NULL, NULL, NULL, NULL, 1, 1, NULL, 'bad block type', NULL, NULL);

src/msgs/system_errors2.sql

@@ -938,6 +938,7 @@ set bulk_insert INSERT INTO SYSTEM_ERRORS (SQL_CODE, SQL_CLASS, SQL_SUBCLASS, FA
 (-901, '22', '023', 0, 929, 'tom_rsa_verify', NULL, NULL)
 (-901, '22', '023', 0, 930, 'tom_chacha_key', NULL, NULL)
 (-901, '08', '003', 0, 931, 'bad_repl_handle', NULL, NULL)
+(-901, '0B', '000', 0, 932, 'tra_snapshot_does_not_exist', NULL, NULL)
 -- GFIX
 (-901, '00', '000', 3, 1, 'gfix_db_name', NULL, NULL)
 (-901, '00', '000', 3, 2, 'gfix_invalid_sw', NULL, NULL)

src/yvalve/keywords.cpp

@@ -317,6 +317,7 @@ static const TOK tokens[] =
 	{TOK_NULLIF, "NULLIF", true},
 	{TOK_NULL, "NULL", false},
 	{TOK_NULLS, "NULLS", true},
+	{TOK_NUMBER, "NUMBER", true},
 	{TOK_NUMERIC, "NUMERIC", false},
 	{TOK_OCTET_LENGTH, "OCTET_LENGTH", false},
 	{TOK_OF, "OF", false},