Re: Patch: Write Amplification Reduction Method (WARM)

On Thu, Mar 16, 2017 at 12:53 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:

> On Wed, Mar 15, 2017 at 3:44 PM, Pavan Deolasee
> <pavan(dot)deolasee(at)gmail(dot)com> wrote:
> > I couldn't find a better way without a lot of complex infrastructure.
> Even
> > though we now have ability to mark index pointers and we know that a
> given
> > pointer either points to the pre-WARM chain or post-WARM chain, this does
> > not solve the case when an index does not receive a new entry. In that
> case,
> > both pre-WARM and post-WARM tuples are reachable via the same old index
> > pointer. The only way we could deal with this is to mark index pointers
> as
> > "common", "pre-warm" and "post-warm". But that would require us to update
> > the old pointer's state from "common" to "pre-warm" for the index whose
> keys
> > are being updated. May be it's doable, but might be more complex than the
> > current approach.
>
> /me scratches head.
>
> Aren't pre-warm and post-warm just (better) names for blue and red?
>
>
Yeah, sounds better. Just to make it clear, the current design sets the
following information:

HEAP_WARM_TUPLE - When a row gets WARM updated, both old and new versions
of the row are marked with HEAP_WARM_TUPLE flag. This allows us to remember
that a certain row was WARM-updated, even if the update later aborts and we
cleanup the new version and truncate the chain. All subsequent tuple
versions will carry this flag until a non-HOT updates happens, which breaks
the HOT chain.

HEAP_WARM_RED - After first WARM update, the new version of the tuple is
marked with this flag. This flag is also carried forward to all future HOT
updated tuples. So the only tuple that has HEAP_WARM_TUPLE but not
HEAP_WARM_RED is the old version before the WARM update. Also, all tuples
marked with HEAP_WARM_RED flag satisfies HOT property (i.e. all index key
columns share the same value). Similarly, all tuples NOT marked with
HEAP_WARM_RED also satisfy HOT property. I've so far called them Red and
Blue chains respectively.

In addition, in the current patch, the new index pointers resulted from
WARM updates are marked BTREE_INDEX_RED_POINTER/HASH_INDEX_RED_POINTER

I think per your suggestion we can change HEAP_WARM_RED to HEAP_WARM_TUPLE
and similarly rename the index pointers to BTREE/HASH_INDEX_WARM_POINTER
and replace HEAP_WARM_TUPLE with something like HEAP_WARM_UPDATED_TUPLE to
signify that this or some previous version of this chain was once
WARM-updated.

Does that sound ok? I can change the patch accordingly.

Thanks,
Pavan

--
Pavan Deolasee http://www.2ndQuadrant.com/
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