The following steps describe how the SQL Remote Message Agent (dbremote) applies incoming messages:
It reads the messages. Messages are read and the header information is examined (to determine the correct order of application). Reading messages from the message system is single-threaded.
It applies the messages. Read messages are passed off to database worker threads to be applied.
On remote databases, the messages are usually applied serially. In a multi-tier system, a remote database can also be a consolidated database for other remotes. On this type of a remote database, the messages are applied as on a consolidated database.
On the consolidated database, the default is to apply the messages serially. You can use additional database worker threads to apply incoming messages from remote users in parallel. See the -w option in SQL Remote Message Agent utility (dbremote).
When database worker threads are used on a consolidated database:
Messages from different remote users are applied in parallel.
Messages from a single remote user are applied serially.
For example, ten messages from a single remote user are applied by a single worker thread in the correct order.
Advantages of using database worker threads Disadvantages of using database worker threadsUsing database worker threads on the consolidated database can decrease throughput if they cause a lot of locking between users.
A deadlock is handled by re-applying the rolled-back transaction later.
Set the number of database worker threadsOn the consolidated database, use the -w option to set the number of database worker threads.
For example, the following command sets the number of worker threads to 5:
dbremote -c "DSN=SQL Anywhere 12 Demo" -w 5 |
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