Re: Add generate_series(numeric, numeric)

2014-12-15 10:25 GMT+07:00 Andrew Gierth <andrew(at)tao11(dot)riddles(dot)org(dot)uk>:
>
> >>>>> "Fujii" == Fujii Masao <masao(dot)fujii(at)gmail(dot)com> writes:
>
> Fujii> Pushed.
>
> Bug found:
>
> regression=# select count(*) from generate_series(1::numeric,10) v,
> generate_series(1,v) w;
> count
> -------
> 99990
> (1 row)
>
> regression=# select count(*) from generate_series(1::numeric,10) v,
> generate_series(1,v+0) w;
> count
> -------
> 55
> (1 row)
>
> The error is in the use of PG_GETARG_NUMERIC and init_var_from_num
> when setting up the multi-call state; init_var_from_num points at the
> original num's digits rather than copying them, but start_num and
> stop_num have just been (potentially) detoasted in the per-call
> context, in which case the storage will have been freed by the next
> call.
>

Oops.

Obviously this could also be fixed by not detoasting the input until
> after switching to the multi-call context, but it looks to me like
> that would be unnecessarily complex.
>
> Suggested patch attached.
>

Thanks

> (Is it also worth putting an explicit warning about this kind of thing
> in the SRF docs?)
>

I think yes, it will be good. The alternative is restructuring this
paragraph in the SRF docs:

The memory context that is current when the SRF is called is a transient
> context that will be cleared between calls. This means that you do not need
> to call pfree on everything you allocated using palloc; it will go away
> anyway. However, if you want to allocate any data structures to live across
> calls, you need to put them somewhere else. The memory context referenced
> by multi_call_memory_ctx is a suitable location for any data that needs
> to survive until the SRF is finished running. In most cases, this means
> that you should switch into multi_call_memory_ctx while doing the
> first-call setup.
>

The important part "However, if you want to allocate any data structures to
live across calls, you need to put them somewhere else." is buried in the
docs.

But i think explicit warning is more noticeable for new developer like me.

Regards,
--
Ali Akbar