postgres fulled my disk

Under the base/database directory, there are so many pg_psort*,
pg_btsort*, and HJ* files.
They ate all my 8GB disk. What are they? why did they appear?
And What should I do?

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Science is the game we play with God to find out what his rules are.
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Doo Suk Yang
Research Scientist Voice: 82-42-866-2222
LG Chemical Ltd. Research Park
Biotech Research Institute I FAX: 82-42-861-2566
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A fool hath no delight in understanding, but that his heart may discover itself.
(Proverbs 18:2)
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