Many of the readers of my blog have an equal interest in the "client side". You'll be happy that Oracle Instant Client 18.3 for Linux 64-bit and 32-bit is also available. Instant Client is just a rebundling of the Oracle client libraries and some tools. They are the same ones available with an Oracle Database installation or the "full" Oracle Client installation but installation is much simpler: you just unzip a file, or install an RPM package on Linux and use them to connect your applications to Oracle Database.
The "Oracle Client", in whatever install footprint you choose, covers a number of technologies and provides a lot of language APIs. The Instant Client packages contain these APIs and selected tools like SQL*Plus and Data Pump. I'll let those teams blow their own trumpets about the new release. Here I'll talk about some of the Oracle Client functionality that benefits the Oracle Oracle Call Interface (OCI) API for C programs, and all the scripting languages that use OCI:
My wider group's most exciting project in 18.3 is the Connection Manager (CMAN) Traffic Director mode whose sub-location in the Oracle manual is a sign of how the feature its transparent, and not indicative of the huge engineering effort that went into it. CMAN in Traffic Director Mode is a proxy between the database clients and the database instances. Supported OCI clients from Oracle Database 11g Release 2 (11.2) and later can connect to CMAN to get improved high availability (HA) for planned and unplanned database server outages, connection multiplexing support, and load balancing.
Cherry picking some notable Oracle Client 18c features that are available via OCI:
You probably know that Oracle Database 18c is really just a re-badged 220.127.116.11. Due to the major version number change and the new release strategy, there is a new OCIServerRelease2() call to get the database version number. The old OCIServerRelease() function will give just the base release information so use the new function to get the actual DB patch level. Why? Let's just say there were robust discussions about the upgrade and release cycles, and about handling the "accelerated" version change across the whole database product suite and how things like upgrade tools were affected.
Extracting Instant Client 18.3 ZIP files now pre-creates symbolic links for the C and C++ client libraries on relevant operating systems. Yay! One fewer install step.
Instant Client now also pre-creates a network/admin sub-directory to show where you can put any optional network and other configuration files such as tnsnames.ora, sqlnet.ora, ldap.ora, and oraaccess.xml. This directory will be used by default for any application that loads the related Oracle Client libraries.
Support for Client Result Caching with dynamic binds where descriptors are not involved and the bind length is less than 32768. Since scripting languages tend to use dynamic binds for character data this could be a big performance win for your lookup table queries.
Unique ID generation improvements. One little old gotcha, particularly in some hosted or cloud environments, were errors when Oracle applications tried to generate a unique key for your client. This manifested itself as an Oracle error when you tried to start a program. Workarounds included adding a hostname to /etc/hosts. There were improvements in Oracle Client 18c for unique key generation so the problem should be less common.
A new call timeout parameter can be enabled for C applications. This applies to post-connection round-trips to the database, making it easier to interrupt long running calls and satisfy application quality of service requirements. After you connect, each OCI call may make one of more round-trips to Oracle database:
If the time from the start of any one round-trip to the completion of that same round-trip exceeds the call timeout milliseconds, then the operation is halted and an Oracle error is returned.
In the case where an OCI call requires more than one round-trip and each round-trip takes less than the specified number of milliseconds, then no timeout will occur, even if the sum of all round-trip calls exceeds the call timeout value.
If no round-trip is required, the operation will never be interrupted.
After a timeout has occurred, the connection must be cleaned up. This is allowed to run for the same amount of time as specified for the original timeout. For very small timeouts, if the cleanup fails, then an ORA-3114 is returned and the connection must be released. However if the cleanup is successful then an ORA-3136 is returned and the application can continue using the connection.
You can see this will be most useful for interrupting SQL statements whose "execute" phase may take some time.
The OCI Session pool underlays many application connection pools (and if it doesn't underlay yours, then it should - ask me why). Improvements in 18c session pooling include some usability "do-what-I-mean" parameter size check tweaks, internal lock improvements, and a new attribute OCI_ATTR_SPOOL_MAX_USE_SESSION.
One other change that was much debated during development is the OCISessionGet() behavior of OCI_SPOOL_ATTRVAL_NOWAIT mode when a pool has to grow. Prior to 18c, even though it was a 'no wait' operation, getting a connection would actually wait for the pool to grow. Some users didn't like this. Since creating connections could take a few moments they had no way to control the quality of service. Now in 18c the mode doesn't wait - if there's no free connection immediately available, then control is returned to the application with an error. If you are impacted by the new behavior, then look at using alternative session acquire modes like OCI_SPOOL_ATTRVAL_TIMEDWAIT. Or better, keep your pool a constant size so it doesn't need to grow, which is what is recommended by Oracle's Real World Performance Group.
SODA support. Simple Oracle Document Access (SODA) that was previously only available via JDBC is now available in OCI. Yum. Let's see what we can do with this now it's in C. More on this later.
I hope this has given you a taste of some Oracle Client 18c changes and given you links to explore more. Don't forget that much new database functionality is available to clients transparently or via SQL and PL/SQL.
Finally, remember that Oracle has client-server version interoperability so 18c OCI programs can connect to Oracle Database 11.2 or later. It's time to upgrade your client!