From: | Bruce Momjian <bruce(at)momjian(dot)us> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | Tatsuo Ishii <ishii(at)postgresql(dot)org>, mike(at)fuhr(dot)org, pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: What is the maximum encoding-conversion growth rate, anyway? |
Date: | 2008-03-11 19:45:01 |
Message-ID: | 200803111945.m2BJj2w09898@momjian.us |
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Thread: | |
Lists: | pgsql-hackers |
Added to TODO:
* Change memory allocation for multi-byte functions so memory is
allocated inside conversion functions
Currently we preallocate memory based on worst-case usage.
---------------------------------------------------------------------------
Tom Lane wrote:
> Tatsuo Ishii <ishii(at)postgresql(dot)org> writes:
> > Thinking more, it striked me that users can define arbitarily growing
> > rate by using CFREATE CONVERSION. So it seems we need functionality to
> > define the growing rate anyway.
>
> Seems to me that would be an argument for moving the palloc inside the
> conversion functions, as I suggested before.
>
> In practice though, I find it hard to imagine a pair of encodings for
> which the growth rate is more than 3x. You'd need something that
> translates a single-byte character into 4 or more bytes (pretty
> unlikely, especially considering we require all these encodings to be
> ASCII supersets); or something that translates a 2-byte character into
> more than 6 bytes.
>
> regards, tom lane
>
> ---------------------------(end of broadcast)---------------------------
> TIP 9: In versions below 8.0, the planner will ignore your desire to
> choose an index scan if your joining column's datatypes do not
> match
--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://postgres.enterprisedb.com
+ If your life is a hard drive, Christ can be your backup. +
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