On Wed, Jan 6, 2010 at 6:11 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> I wrote:
>> With this patch, a CLOBBER_CACHE_ALWAYS build starts falling apart all
>> over the place :-(. Looks like you blew the memory management somehow;
>> it appears to be using a previously pfree'd pointer:
>
> Actually, there were three different problems there:
>
> 1. Relying on a HASH_REMOVE'd hashtable entry to still be present and
> valid. This is at least bad style. I wonder if we should tweak the
> dynahash code to memset a free'd entry to 7F's like pfree does.
Oops.
> 2. Assuming that a cache entry will remain in existence across a catalog
> access. This will work except when it doesn't, ie, when a cache flush
> occurs during the table access. You've just learned the hard way what
> CLOBBER_CACHE_ALWAYS testing is good for ;-)
Yeah. I tried that at an earlier stage of development, but obviously
I should have retested with the final version.
> 3. Invoking tablespace_reloptions while switched into
> CacheMemoryContext. This isn't a crasher, but it strikes me as a bad
> idea because if reloptions.c happens to leak anything, that'll represent
> a permanent (session-lifespan) memory leak. And it's complicated enough
> that being sure it doesn't leak anything is hard. I think you should
> invoke tablespace_reloptions in the caller's memory context, and then if
> it succeeds, copy the result into CacheMemoryContext. That would
> probably require fixing the problem you noted earlier today about
> making TableSpaceOpts be a valid bytea value, so that it'll be easy to
> copy (then you can use datumCopy, for instance).
Hmm. That seems a little crufty, but it makes sense. Will do.
> I fixed the first two because they were in the way of investigating
> another problem, but #3 still needs your attention.
Thanks, and sorry for the hassle.
...Robert
