Re: Heap WARM Tuples - Design Draft

On Thu, Aug  4, 2016 at 06:16:02PM +0100, Simon Riggs wrote:
> On 4 August 2016 at 18:05, Bruce Momjian <bruce@momjian.us> wrote:
> 
> >> Approach 2 seems more reasonable and simple.
> >>
> >> There are only 2 bits for lp_flags and all combinations are already used. But
> >> for LP_REDIRECT root line pointer, we could use the lp_len field to store this
> >> special flag, which is not used for LP_REDIRECT line pointers. So we are able
> >> to mark the root line pointer.
> >
> > Uh, as I understand it, we only use LP_REDIRECT when we have _removed_
> > the tuple that the ctid was pointing to, but it seems you would need to
> > set HEAP_RECHECK_REQUIRED earlier than that.
> 
> Hmm. Mostly there will be one, so this is just for the first update
> after any VACUUM.
> 
> Adding a new linepointer just to hold this seems kludgy and could mean
> we run out of linepointers.

Ah, so in cases where there isn't an existing LP_REDIRECT for the chain,
you create one and use the lp_len to identify it as a WARM chain?  Hmm.

You can't update the indexes pointing to the existing ctid, so what you
would really have to do is to write over the existing ctid with
LP_REDIRECT plus WARM marker, and move the old ctid to a new ctid slot?

--  Bruce Momjian  <bruce@momjian.us>        http://momjian.us EnterpriseDB
http://enterprisedb.com

+ As you are, so once was I. As I am, so you will be. +
+                     Ancient Roman grave inscription +