Differences between Oracle JDBC Thin and Thick Drivers

Question

If any body is looking for this information...
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I have a question concerning the Oracle JDBC thin vs. thick drivers
and how they might affect operations from an application perspective.
We're in a Solais 8/Oracle 8.1.7.2 environment. We have several
applications on several servers connecting to the Oracle database.
For redundancy, we're looking into setting up TAF (transparent
application failover). Currently, some of our apps use the Oracle
<B>JDBC thin</B> drivers to talk to the database, with a connection
string that like this:
<B> jdbc:oracle:thin:@host:port:ORACLE_SID </B>
In a disaster recovery mode, where we would switch the database
from one server to another, the host name in the above string
would become invalid. That means we have to shut down our application
servers and restart them with an updated string.
Using the Oracle <B>OCI (thick)</B> driver though, allows us to connect
to a Net8 service instead of a specific server:
<B> jdbc:oracle:oci8:@NET8_SERVICE_NAME </B>
Coupled with the FAILOVER=ON option configured in Net8, it is
then possible to direct a connection from the first server to
the failover database on another server. This is exactly what
we would like to do.
My question is, from an application perspective, how is the Oracle
thick driver different from the thin driver? If everything
else is "equal" (i.e. the thick driver is compatible with the
app servers) would there be something within the the thick/OCI
driver that could limit functionality vs. the thin driver?
My understand, which obviously is sketchy, is that the thick
driver is a superset of the thin driver. If this is the case,
and for example if all database connections were handled through
a configuration file with the above OCI connection string, then
theoretically the thick driver should work.
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<B>
In the case with the Oracle, they provide a thin driver that is a 100% Java driver for client-side use without the need of an Oracle installation (maybe that's why we need to input server name and port number of the database server). This is platform indipendent, and has good performance and some features.
The OCI driver on the other hand is not java, require Oracle installation, platform dependent, performance is faster, and has a complete list of all the features.
</B>
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I hope this is what you expect.
JDBC OCI client-side driver: This is a JDBC Type 2 driver that uses Java native methods to call entrypoints in an underlying C library. That C library, called OCI (Oracle Call Interface), interacts with an Oracle database. <B>The JDBC OCI driver requires an Oracle (7.3.4 or above) client installation (including SQL*Net v2.3 or above) and all other dependent files.</B> The use of native methods makes the JDBC OCI driver platform specific. Oracle supports Solaris, Windows, and many other platforms. This means that the Oracle JDBC OCI driver is not appropriate for Java applets, because it depends on a C library to be preinstalled.
JDBC Thin client-side driver: This is a JDBC Type 4 driver that uses Java to connect directly to Oracle. It emulates Oracle's SQL*Net Net8 and TTC adapters using its own TCP/IP based Java socket implementation. <B>The JDBC Thin driver does not require Oracle client software to be installed, but does require the server to be configured with a TCP/IP listener. Because it is written entirely in Java, this driver is platform-independent.</B> The JDBC Thin driver can be downloaded into any browser as part of a Java application. (Note that if running in a client browser, that browser must allow the applet to open a Java socket connection back to the server.
JDBC Thin server-side driver: This is another JDBC Type 4 driver that uses Java to connect directly to Oracle. This driver is used internally by the JServer within the Oracle server. This driver offers the same functionality as the client-side JDBC Thin driver (above), but runs inside an Oracle database and is used to access remote databases. Because it is written entirely in Java, this driver is platform-independent. There is no difference in your code between using the Thin driver from a client application or from inside a server.
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How does one connect with the JDBC Thin Driver?
The the JDBC thin driver provides the only way to access Oracle from the Web (applets). It is smaller and faster than the OCI drivers, and doesn't require a pre-installed version of the JDBC drivers.
import java.sql.*;
class dbAccess {
public static void main (String args []) throws SQLException
DriverManager.registerDriver (new oracle.jdbc.driver.OracleDriver());
Connection conn = DriverManager.getConnection
("jdbc:oracle:thin:@qit-uq-cbiw:1526:orcl", "scott", "tiger");
// @machineName:port:SID, userid, password
Statement stmt = conn.createStatement();
ResultSet rset = stmt.executeQuery("select BANNER from SYS.V_$VERSION");
while (rset.next())
System.out.println (rset.getString(1)); // Print col 1
stmt.close();
How does one connect with the JDBC OCI Driver?
One must have Net8 (SQL*Net) installed and working before attempting to use one of the OCI drivers.
import java.sql.*;
class dbAccess {
public static void main (String args []) throws SQLException
try {
Class.forName ("oracle.jdbc.driver.OracleDriver");
} catch (ClassNotFoundException e) {
e.printStackTrace();
Connection conn = DriverManager.getConnection
("jdbc:oracle:oci8:@qit-uq-cbiw_orcl", "scott", "tiger");
// or oci7 @TNSNames_Entry, userid, password
Statement stmt = conn.createStatement();
ResultSet rset = stmt.executeQuery("select BANNER from SYS.V_$VERSION");
while (rset.next())
System.out.println (rset.getString(1)); // Print col 1
stmt.close();
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Answer 1

Wow, not sure what your question was, but there sure was a lot of information there...
There really is only one case where failover occurs, and it would not normally be in a disaster recovery situation, where you define disaster recovery as the obliteration of your current server farm, network and concievably the operational support staff. This would require a rebuild of your server, network etc and isn't something done with software.
Fail over is normally used for high availablity that would take over in case of hardware server failure, or when your support staff wants to do maintenance on the primary server.
Using the thin and thick driver should have ZERO affect on a failover. Transparent failover will make the secondary server the same IP as the primary, therefore the hostname will still point to the appropriate server. If you are doing this wrong, then you will have to point all your applications to a new IP address. This should be something that you tell your management is UNACCEPTABLE in a fail-over situation, since it is almost sure to fail to fail-over.
You point out that you are providing the TNSNAME, rather than the HOSTNAME when using the thick driver. That's true within your application, but that name is resolved to either a HOSTNAME, or IP ADDRESS before it is sent to the appropriate Oracle server/instance. It is resolved using either a NAME server (same as DNS server but for Oracle), or by looking at a TNSNAMES file. Since the TNSNAMES files profilerate like rabbits within an organization you don't want a fail over that will make you find and switch all the entries, so you must come up with a fail over that does not require it.
So, the application should not be concerned with either the hostname, or the IP address changing during fail over. That makes use of the thin or thick client acceptable for fail over.
Don't know if this will help, but this shows the communication points.
THIN DRIVER
client --> dns --> server/port --> SID
THICK DRIVER
client --> names server --> dns --> server/port --> SID
client --> tnsnames     --> dns --> server/port --> SID