Обсуждение: psql & query string length
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
"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