Re: Cache last known per-tuple offsets to speed long tuple

Thank you for advice.
I am going to remake a patch, in order to make it simple.
The plan of a new patch is as follows.

(1)Add fields to TupleTableSlot and TupleTableData.
This fields are for holding the tuple disassembly information.

(2)Add the codes which initializes/cleans new fields.
These codes are added to execTuples.c.

(3)Add two functions to execQual.c.
One function is just like heap_deformtuple. It is given a
TupleTableSlot. And it extracts the field of tuple incrementary
using the new fields of TupleTableSlot.

The meaning of incrementary is as the following example.
Example: The tupple has 100 columns.
- first call to get col5 will fill first 5 positions in the array.
- next call to get col75 will fill starts from 5 and up to 75.
- next call to get col60 will only refer to array, because
already extracted.

Another function is just like heap_getattr and fast_getattr.
It is given a TupleTableSlot. And this function uses new
function(like a heap_deformtuple), instead of nocachegetattr.

(4)ExecEvalVar uses new function(like a heap_getattr) instead of
heap_getattr.

With a new patch, only three files of tuptable.h, and execTuple.c
and execQual.c are due to be changed.

> BTW, why is it that your profile shows *more* calls to
> heap_deformtuple_incr after the patch than there were nocachegetattr
> calls before?

Many one is for printtup.
(printtup -> heap_deformtuple -> heap_deformtuple_incr)
Since the code of heap_deformtuple and heap_deformtuple_incr has been
share, heap_deformtuple_incr looks many calls than nocachegetattr.

If a part for the number of calls of heap_deformtuple_incr
by printtup is removed, heap_deformtuple_incr and nocachegetattr
will be the same number of calls.

With my test being to access the column in ascending order
(select t100, t110 ...), heap_deformtuple_incr and nocachegetattr
is the same calls.
If the column is accessed in descending order(select t200, t190...),
number of calls of heap_deformtuple_incr will decrease sharply.
It is because a result is cached by the first call to get t200.

regards,

--- Atsushi Ogawa
a_ogawa(at)hi-ho(dot)ne(dot)jp