Databases Reference
In-Depth Information
The increase in the number of packets also means an increase in packet over-
head. High packet overhead reduces throughput, or the amount of data that is
transferred from sender to receiver over a period of time.
Why does packet overhead reduce throughput? Each packet stores extra
bytes of information in the packet header, which limits the amount of data that
can be transported in each packet. The smaller the packet size, the more packets
are required to transport data. For example, a 64KB packet with a packet header
of 30 bytes equals a total of three 32KB packets, each with 30-byte packet head-
ers, as shown in Figure 4-8. The extra CPU required to disassemble packets for
transport and reassemble them when they reach their destination reduces the
overall transmission speed of the raw data. Fewer packets require less disassem-
bly and reassembly, and ultimately, use less CPU.
Database Server:
Packet Size = 64KB
Database Driver:
Packet Size = 32KB
Header (30 Bytes)
Header (30 Bytes)
Header (30 Bytes)
Header (30 Bytes)
Data (31.971KB)
Data (31.971KB)
Data (.029KB)
Data (63.971KB)
Figure 4-8
64KB database protocol packets compared to 32KB packets
Once database protocol packets are created, the database driver hands over the
packets to TCP/IP for transfer to the database server. TCP/IP transfers the data in
network packets
. If the size of the database protocol packet is larger than the
defined size of the network packet, TCP/IP breaks up the communication into
even smaller network packets for transmission over the network and reassembles
them at their destination.
Think of it like this: The database protocol packet is like a case of diet soda,
which can be too difficult to carry over a long distance. TCP/IP breaks up that
case into four 6 packs, or network packets, that can be easily carried over the
network. When all four 6 packs reach their destination, they are reassembled
into a case.
