Fixed CORE-2478: mon$memory_usage: Incorrect database memory reported on CS and SC.

doc/README.monitoring_tables

@@ -224,6 +224,9 @@ Monitoring tables
         record has these columns populated with non-zero values. Small allocations don't go
         to the OS level, they're redirected to the database memory pool instead. So usually
         only MON$DATABASE and memory-bound objects point to non-zero "allocated" values.
+      - the counter set linked to a record in MON$DATABASE reports the memory shared among
+        all attachments. In Classic and SuperClassic, these counters are zero meaning no
+        shared cache in these architectures.
 
     6) For table MON$CONTEXT_VARIABLES:
       - column MON$ATTACHMENT_ID contains a valid ID only for session-level context variables.

src/jrd/DatabaseSnapshot.cpp

@@ -65,6 +65,12 @@
 #include <windows.h>
 #endif
 
+#ifdef SUPERSERVER
+const bool sharedDbb = true;
+#else
+const bool sharedDbb = false;
+#endif
+
 
 using namespace Firebird;
 using namespace Jrd;
@@ -880,7 +886,16 @@ void DatabaseSnapshot::putDatabase(const Database* database, Writer& writer, int
 	record.storeGlobalId(f_mon_db_stat_id, getGlobalId(stat_id));
 	writer.putRecord(record);
 	putStatistics(database->dbb_stats, writer, stat_id, stat_database);
-	putMemoryUsage(database->dbb_memory_stats, writer, stat_id, stat_database);
+
+	if (sharedDbb)
+	{
+		putMemoryUsage(database->dbb_memory_stats, writer, stat_id, stat_database);
+	}
+	else
+	{
+		MemoryStats zero_stats;
+		putMemoryUsage(zero_stats, writer, stat_id, stat_database);
+	}
 }
 
 
@@ -945,7 +960,15 @@ bool DatabaseSnapshot::putAttachment(const Attachment* attachment, Writer& write
 	record.storeGlobalId(f_mon_att_stat_id, getGlobalId(stat_id));
 	writer.putRecord(record);
 	putStatistics(attachment->att_stats, writer, stat_id, stat_attachment);
-	putMemoryUsage(attachment->att_memory_stats, writer, stat_id, stat_attachment);
+
+	if (sharedDbb)
+	{
+		putMemoryUsage(attachment->att_memory_stats, writer, stat_id, stat_attachment);
+	}
+	else
+	{
+		putMemoryUsage(attachment->att_database->dbb_memory_stats, writer, stat_id, stat_attachment);
+	}
 
 	return true;
 }