Databases Reference
In-Depth Information
The network path analysis revealed that when the application requested
data, network packets associated with requests typically made as many as 17 net-
work hops before reaching the database server. Although the client and database
server machines resided in the same location, they were assigned to different cor-
porate network subnets. In this case, reassigning the machines to the same net-
work subnet reduced the number of network hops from 17 to 1, and the average
response time for bulk updates decreased from 30 seconds to 5 seconds, an
amazing performance gain of 500%.
Note
A
virtual private network (VPN)
emulates a private data network for
applications that transfer data over the Internet. It doesn't eliminate net-
work hops but provides a secure extension of a private network and
reduces network contention.
Before we go forward, let's recap some of what we've already learned about how
database drivers and database servers use the network to request and send data:
•
Database drivers and database servers communicate by sending database
protocol packets.
•
If the size of the database protocol packet is larger than the defined size of
the network packet, TCP/IP divides the database protocol packets into as
many network packets as needed for transmission over the network.
•
The MTU is the maximum network packet size that can be sent across a par-
ticular network link and is a characteristic of the network type.
•
Packet size is important for both types of packets because the fewer the
packets, the better the performance.
Packet fragmentation
occurs when a network packet is too large to traverse
a network link as determined by the network link's MTU. For example, if a net-
work link's MTU is 1500 bytes, it cannot transport a 1700-byte packet. An over-
sized packet must be divided into smaller packets that are able to traverse the
link, or the communication must be re-sent using smaller packets.
