Thanks Graig and I��m now have more confidence on sharing connections among
servlets
The reasons behind why I have to build my connection pool instead of using
common ones are:
- The hit rate of my app will be very large and all servlet operations
(doGet/doPost) require many database queries and updates
- each connection in Oracle requires around 70M memory and so seems
difficult to built a large pool
- all updates are auto-commit
- heard that connection will hold resources in Oracle if connection
keep open for sometime, so I have to refresh (release and re-connect)
connections periodically and I don��t known whether existing connection pool
implementations have taken care about that
- heard that connection will timeout if not used for long time, so I
have to set periodic task to do dummy operation
I really don��t want to write my own connection pool but can anyone help to
clear my concerns.
Thanks in advance
Kenneth
-----Original Message-----
From: Craig R. McClanahan [mailto:[EMAIL PROTECTED]]
Sent: Friday, December 03, 1999 12:38 AM
To: [EMAIL PROTECTED]
Subject: Re: Two simultaneous statements in the same
connection.
"Kwan, Kenneth Y" wrote:
> So, does anyone know that Oracle 8i JDBC OCI driver can support
concurrent
> statements on the same connection, e.g. connection which is shared
by many
> servlets ?
>
There are really two issues here.
Yes, the Oracle drivers support multiple active statements per
connection. The
connection can be shared by many servlets -- a very convenient way
is to store
the open connection as a servlet context attribute
(ServletContext.setAttribute()).
However, you need to consider what happens when more than one person
is using
your servlet-based application. If they are all using the same
connection, the
fact that you have multiple statements works fine, up until the
point where you
do a COMMIT or ROLLBACK for a user. At that point, the database
transaction
which is running is completed -- and this affects *all* of the
users, whether
they are through or not! Database transactions are global to a
connection.
This is one of the reasons that connection pools were created. The
idea is
that, within a single response, you follow this kind of a design
pattern:
* Allocate a connection from the pool
* Do all the database work you need
* Do a COMMIT or ROLLBACK
* Return the connection to the pool
In this way, the database accesses from different simultaneous users
do not
interfere with each other, because they are running in different
transactions.
Within a particular transaction, you can still have multiple
statements open if
you need them (because Oracle supports this), but they will all be
aimed at
performing part of a single overall process.
There have been tons of discussions about connection pools on this
list, along
with sources for several versions of them. See the list archives
(http://archives.java.sun.com) for details, or check some of the FAQ
sites.
>
> Kenneth
>
Craig McClanahan
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