psql & query string length

In implementing a core Text C++ class object,
we use realloc() without problems. However, with
regard to resizing, we always DOUBLE the existing
size of the buffer when the string needs to be
expanded so that it doesn't take 100 iterations
(and therefore 100 realloc()'s) to create an 800K
buffer.

Hope this helps,

M. Mascari

--- "Ansley, Michael" <Michael.Ansley@intec.co.za>
wrote:

Hi,

Well, I got psql to do it's thing, eventually. I've
tested it for pretty
much everything, including \e, \g, \r, \i.
The one problem that I have had is that after about
the third '\i long.sql',
I get a core dump, because sprintf moaned about
string size complications.
The way I have structured it, memory is reallocated
(re- malloc'd, not
realloc'd) every time the query is extended. I
suspect that this is very
inefficient, and probably causing the system to
hooch after loading long.sql
three times. The main thought that I have had is to
extend the query buffer
in blocks of about 8k or 16k. I presume that once
working with set memory
sizes, the memory usage will be substantially more
efficient. Ideas?

Also, what's the deal with realloc? I tried it a
couple of times, but it
really screwed me around (hence the re- malloc'ing).
Or is it just a Bad
Move to use realloc?

MikeA

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"Ansley, Michael" <Michael.Ansley@intec.co.za> writes:

The way I have structured it, memory is reallocated (re- malloc'd, not
realloc'd) every time the query is extended. I suspect that this is very
inefficient,

Probably. You should normally expand by a significant amount each time
you reallocate an expansible buffer, just to avoid making too many
demands on malloc. The method I favor is to double the buffer size at
each realloc step.

and probably causing the system to hooch after loading long.sql
three times.

... but not doing so shouldn't cause a coredump. I bet a plain old
bug is involved here, like writing past the end of the space you do
have allocated.

Also, what's the deal with realloc? I tried it a couple of times, but it
really screwed me around (hence the re- malloc'ing). Or is it just a Bad
Move to use realloc?

realloc is perfectly fine ... see above for more likely theory.

On some old pre-ANSI-standard machines, realloc(NULL, ...) does not
work, so for portability's sake you ought to only use realloc to
increase the size of an existing buffer.

regards, tom lane