Table of Contents
By default, write operations cannot be performed on a replication client site. Replication Manager provides automatic write forwarding as a configurable option for applications with simple data and transaction models. (See the Configuring for Write Forwarding section in the Berkeley DB Programmer's Reference Guide for more information.)
In this chapter, we configure write forwarding for the simple transaction-protected DB application that you created in the Transactional Application chapter.
Write forwarding simplifies adding replication to the stock market quotes database application. Once write forwarding is configured, this application allows any site to accept stock quote updates. There is no need to confine write operations to the master or even to know which site is the master.
The application operates by presenting you with a command line prompt. You then enter the stock symbol and its value, separated by a space. The application takes this information and writes it to the database.
To see the contents of the database, simply press
return at the command prompt.
To quit the application, type 'quit' or 'exit' at the command prompt.
For example, the following illustrates the application's usage. In it, we use entirely fictitious stock market symbols and price values.
node01> java db.repquote_gsg.RepQuoteWrforExampleGSG -h env_home_dir -L \
node01:5000
QUOTESERVER> stock1 88
QUOTESERVER> stock2 .08
QUOTESERVER>
Symbol Price
====== =====
stock1 88
stock2 .08
where L is used to identify the local site
as group creator, which creates the database and starts
this site as master.
With write forwarding, we can add a new stock value in the client site. In the client site (node02), specify the new local client site and the existing remote site in the replication group.
node02> java db.repquote_gsg.RepQuoteWrforExampleGSG -l \
node02:5001 -r node01:5000
QUOTESERVER> stock3 99
QUOTESERVER>
Symbol Price
====== =====
stock1 88
stock2 .08
stock3 99
QUOTESERVER> quit
Finally, verify that the stock3 value replicated
to the master:
QUOTESERVER>
Symbol Price
====== =====
stock1 88
stock2 .08
stock3 99
QUOTESERVER> quit