Thank you Darrick S, vhari, steveg for your article on Laddered Concurrent Connect (LCC): Client Performance Improvements
I didn't quite catch your explanation :"Once the first successful connect is recognized, any remaining occupied sockets are released (closed). A down node will no longer force the client interface to pause until the wait time interval has expired before it attempts to connect to another node."
Does it mean that each time odbc attempts to connect to Teradata, it's tries to connect to all nodes and the first successful connection determines the connection node ?
Another question : Does the LCC include the load balancing mechanism ? I wonder if the LCC could substitute the F5's load balancing mechanism.
With LCC, the client interface (ODBC in this case) tries to connect to the next node in the COP sequence. If that node responds within the internal time-out limit, no further connects are issued. However, if no response is received, another connect to a randomely selected node will be initiated, up to 9 outstanding connects each temporally separated by a dynamically determined interval. The first node to respond will be rewarded with the session. Under normal circumstances, that should occur for the first connect attempt.
LCC was not designed nor intended to be a load-balancing mechanism, per se. Rather, the objective here was to minimize connect waits by allowing nodes to essentially compete for sessions (and thereby allow down nodes – such as dormant HSNs – to be effectively bypassed while remaining visible via DNS).
Thanks you vhari.
One more question on your article :
I quote : "3. ODBC connects to MULTIPLE nodes based on the a specified Delay Internval"
Can you tell more about the Delay Interval ?
Is it a a parameter in dbscontrol ?
The delay interval was discussed in the paragraph right above the 2nd diagram.
"LCC does not fire off connect requests all at once. Rather, it applies a proprietary dynamic delay interval between connect requests that adjusts according to the previous connect response time. In other words, LCC tries to optimize the delay interval based on current network and server performance characteristics. This means the delay interval will gradually increase if connect responses are relatively slow and decrease if they are relatively fast. "
The delay interval cannot be set externally.