How to tune yum?

[Strong]

I noticed when yum installs something, it gets a LOT of additional
information, for example, it downloads some xml files... My question is
how to "help" it simply to connect to one site, say base or extra and
install the target package with, may, depended ones? My Internet traffic
is very expansive to me so, that additional 1 Mb of spent traffic each
time i want to install say, 300-400 kb package makes this package
unusable for me...
Please, help. Any knowledge/ideas appreciated.

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Best regards,
Strong.