Re: [Drizzle-discuss] Removing Array custom vector allocation for semi-join subqueries

[MARK CALLAGHAN]

On Thu, Feb 26, 2009 at 11:17 PM, Monty Taylor <mordred@stripped> wrote:

> Therefore, I'm going to say that what we _really_ want instead of
> mem_root is what Jay and I have been pushing for for a while - resource
> management through ownership. Pointers to allocated memory should be
> contained in, owned by and managed by an object, such that when the
> object goes away, so does the memory. It's almost like magic how much a
> nice containment hierarchy can achieve the end-goal of mem_root.
>
> I'd post a code sample... but I'm falling asleep sitting here... I'll
> come back to this in the morning. :)
>
> Monty
>

I am curious about how this will deal with the problem of memory
allocations that have different lifetimes. The popular ones in
non-drizzled MySQL are:
* global -- get it from malloc() today
* per connection -- get it from the THDs mem_root today
* per session -- not sure if it exists today
* custom -- not sure if it exists today

Having more than one lifetime is already a problem as you need to be
very careful when maintaining a pointer to an object that has a
shorter lifetime (objects from the global allocation can't point to
per-session, ...).

-- 
Mark Callaghan
mdcallag@stripped