Compression of text fields

[Brian McCane <bmccane(at)mccons(dot)net>]

	I have read somewhere that text fields are "compressed".  What I
am curious about is how the compression of text fields by PostgreSQL might
be affecting the performance of my software.  I currently store entire
copies of documents in a table called "fulltext" as such:

CREATE TABLE fulltext (
    uid		serial8 PRIMARY KEY,
    content	text NOT NULL,
    contentidx	txtidx
) ;

As you can see, I am using contrib/tsearch to find documents for display,
and then I dump out 'content' to the user.

Anyway, when I first created this table, I was concerned about the size of
'content' so I linked my program to zlib and deflate the content field
before storing it into the table.  This means that every time someone
views a document I have to inflate it, also if what I have read is correct
about the text fields, PostgreSQL is trying to deflate/compress/whatever
the field when it stores it so I am duplicating effort.  This probably
slows down the performance of my software, and because compressed
documents are often larger when re-compressed (at least with older
algorithms like LZW) I might be using extra space to store my data.

So:
	1) do text fields get compressed
	2) what compression method is used
	3) is there a way to view actual storage space used versus
	   the value I get from length()
	4) Can I disable the compression to improve storage speed
	   if the compression algorithm is not as good as deflate

- brian

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