About multi process access BDB question

Question

I am designing one system using BDB.I have some questions about multi process access BDB.
1.If there are two process, they are shared BDB cache or every one has self BDB cache? (My understanding is every process has cache by itself.)
2.If one process write BDB and at the same time one process read BDB,how to make read processs can read data which write by write process just now?

Answer 1

1.If there are two process, they are shared BDB cache
or every one has self BDB cache? (My understanding
is every process has cache by itself.)You can configure it either way. The cache is maintained as part of the so-called environment. The usual thing is to configure a shared cache. You need to read about environments in the BDB and BDB/XML documentation.
http://www.oracle.com/technology/documentation/berkeley-db/xml/index.html
2.If one process write BDB and at the same time one
process read BDB,how to make read processs can read
data which write by write process just now?Use transactions, set up deadlock handling, and think about what transaction isolation guarantees you need. Note that there are four different fundamental setups for BDB: DS, CDS, TDS and HA, which stand for Data Store, Concurrent DS, Transactional DS and High Availability. For read-write concurrency, you need TDS.
http://www.oracle.com/technology/documentation/berkeley-db/xml/ref/intro/products.html
For high concurrency at the expense of memory, consider using multi-version concurrency control (MVCC). You can read about it in the following thread, especially in George Feinberg's replies:
Deadlock handling for beginners
In addition, there is ample documentation included in the BDB/XML distribution. It's pretty complex, as BDB can be configured in many different ways.
Michael Ludwig