Re: Re: External search engine, advice

mlw <markw(at)mohawksoft(dot)com> writes:
> The above is an example of how to write a function that returns multiple
> results.

One suggestion: you must check not only that fcinfo->resultinfo isn't
NULL, but that it points at the sort of node you're expecting. Say

if (fcinfo->resultinfo == NULL ||
! IsA(fcinfo->resultinfo, ReturnSetInfo))
<complain>;

If you fail to do this, you can fully expect your code to coredump
a version or two hence. Right now the only possibility for resultinfo
is to point at a ReturnSetInfo, but that *will* change.

> create function ftss_search (varchar)
> returns setof integer
> as '/usr/local/lib/library.so', 'ftss_search'
> language 'c' with (iscachable);

> The above in an example of how one would register this function in postgres.

Hmm ... given that ftss refers to external files, is it a good idea to
mark it cachable? I'd sort of expect that the values it returns for
a particular argument could change over time. Cachable amounts to a
promise that the results for a given argument will not change over time.

regards, tom lane