Re: Heap WARM Tuples - Design Draft

On Sun, Aug  7, 2016 at 10:49:45AM -0400, Bruce Momjian wrote:
> OK, crazy idea time --- what if we only do WARM chain additions when all
> indexed values are increasing (with NULLs higher than all values)?  (If
> a key is always-increasing, it can't match a previous value in the
> chain.)  That avoids the problem of having to check the WARM chain,
> except for the previous tuple, and the problem of pruning removing
> changed rows.  It avoids having to check the index for matching key/ctid
> values, and it prevents CREATE INDEX from having to index WARM chain
> values.
> 
> Any decreasing value would cause a normal tuple be created.

Actually, when we add the first WARM tuple, we can mark the HOT/WARM
chain as either all-incrementing or all-decrementing.  We would need a
bit to indicate that.

Also, it would be possible for keys involved in multi-key indexes to not
match the direction of the chain as long as keys earlier in the index
matched, e.g. key (1,5,6) would be less than (2,1,1) since 1 < 2, even
though 5 > 1.  I am not sure it would be worth detecting this.

--  Bruce Momjian          http://momjian.us EnterpriseDB                             http://enterprisedb.com

+ As you are, so once was I. As I am, so you will be. +
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