Re: [HACKERS] lztext and parser

On Thu, 25 Nov 1999, Jan Wieck wrote:

> Hi,
>
> I'm hacking in the operator functions for the lztext type and
> have a little question.

Hi,

I see your the lztext/pg_compress in CVS and it is *very* nice,
and I have a little comment.

> With the generic per-byte decompressor I added, it would be
> very easy to produce functions like

It's very good if compression routines support data stream. Suppose
you add the pre-byte compressor?

Reasoning: What is fastly - (1) a standard data I/O reading or
(2) a compressed data I/O reading and decompress it
(fast CPU vs. slowly I/O)?

IMHO if (2) is fastly is prabably good for something
data use second way. But I don't know where use this
way in PgSQL :-)

> too. Comparision between lztext and text does already work
> because there are lztext->text and vice versa functions
> available and the parser automatically typecasts.
>
> So would it be a win or a dead end street to provide those
> functions? Does it look for a direct comparision function
> allways first? Then it would be, because it would never
> choose to compress the text item and then compare two
> lztext's (what would be terrible).
>

In the lztext_eq(lztext *lz1, lztext *lz2) you use lztext_cmp().
I'm not sure if it is good, because you must decompress fistly, but
you don't need information about '<' or '>', you need '=' only. Why
you not use memcmp() (or other method) for this, and comparate this
without decompression? Two equal string is equal in a compressed form,
or not?

IMHO in some routines (datetime) in PgSQL I saw internal cache, what
add this to the lztext_cmp(), and not decompress all in each time?

All in this letter is comments and suggestions, you can always remove
this letter to /dev/null :-)

Karel

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