Re: [HACKERS] Index only scan for cube and seg

[Andrey Borodin]

Hi!
> 29 окт. 2017 г., в 2:24, Alexander Korotkov  
> написал(а):
> 
> As I can see, cube GiST code always uses DatumGetNDBOX() macro to transform 
> Datum to (NDBOX *).
> 
> #define DatumGetNDBOX(x)  ((NDBOX *) PG_DETOAST_DATUM(x))
> 
> Thus, it should be safe to just remove both compress/decompress methods from 
> existing opclass.

Alexander, Tom, you are absolutely right. I was sure there is toasting code in 
cube's compress, but it was not ever there.

Here is patch for cube that drops functions.

Best regards, Andrey Borodin.


0001-Enable-Index-Only-Scan-in-cube.patch
Description: Binary data


0001-Enable-Index-Only-Scan-in-seg.patch
Description: Binary data



-- 
Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-hackers

Re: [HACKERS] Index only scan for cube and seg

[Alexander Korotkov]

On Fri, Oct 27, 2017 at 9:54 PM, Tom Lane  wrote:

> Robert Haas  writes:
> > On Thu, Oct 26, 2017 at 12:22 PM, Andrey Borodin 
> wrote:
> >> For cube there is new default opclass.
>
> > I seem to recall that changing the default opclass causes unsolvable
> > problems with upgrades.  You might want to check the archives for
> > previous discussions of this issue; unfortunately, I don't recall the
> > details off-hand.
>
> Quite aside from that, replacing the opclass with a new one creates
> user-visible headaches that I don't think are justified, i.e. having to
> reconstruct indexes in order to get the benefit.
>
> Maybe I'm missing something, but ISTM you could just drop the compress
> function and call it good.  This would mean that an IOS scan would
> sometimes hand back a toast-compressed value, but what's the problem
> with that?
>

+1,
I think in this case replacing default opclass or even duplicating opclass
isn't justified.

(The only reason for making a decompress function that just detoasts
> is that your other support functions then do not have to consider
> the possibility that they're handed a toast-compressed value.  I have
> not checked whether that really matters for cube.)
>

As I can see, cube GiST code always uses DatumGetNDBOX() macro to transform
Datum to (NDBOX *).

#define DatumGetNDBOX(x) ((NDBOX *) PG_DETOAST_DATUM(x))

Thus, it should be safe to just remove both compress/decompress methods
from existing opclass.

--
Alexander Korotkov
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company

Re: [HACKERS] Index only scan for cube and seg

[Tom Lane]

Robert Haas  writes:
> On Thu, Oct 26, 2017 at 12:22 PM, Andrey Borodin  wrote:
>> For cube there is new default opclass.

> I seem to recall that changing the default opclass causes unsolvable
> problems with upgrades.  You might want to check the archives for
> previous discussions of this issue; unfortunately, I don't recall the
> details off-hand.

Quite aside from that, replacing the opclass with a new one creates
user-visible headaches that I don't think are justified, i.e. having to
reconstruct indexes in order to get the benefit.

Maybe I'm missing something, but ISTM you could just drop the compress
function and call it good.  This would mean that an IOS scan would
sometimes hand back a toast-compressed value, but what's the problem
with that?

(The only reason for making a decompress function that just detoasts
is that your other support functions then do not have to consider
the possibility that they're handed a toast-compressed value.  I have
not checked whether that really matters for cube.)

regards, tom lane


-- 
Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-hackers

Re: [HACKERS] Index only scan for cube and seg

[Robert Haas]

On Thu, Oct 26, 2017 at 12:22 PM, Andrey Borodin  wrote:
> For cube there is new default opclass.

I seem to recall that changing the default opclass causes unsolvable
problems with upgrades.  You might want to check the archives for
previous discussions of this issue; unfortunately, I don't recall the
details off-hand.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company


-- 
Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-hackers

[HACKERS] Index only scan for cube and seg

[Andrey Borodin]

Hi hackers!

Here are patches enabling Index Only Scan for cube and seg extensions.

These patches follow this discussion [0].

For cube there is new default opclass. We cannot drop old opclass, because it 
could TOAST come cube values in rare occasions. Index Only Scan is enabled only 
for newly created indexes. Btw I can add fetch to old opclass so that IOS would 
be enabled.
For seg compress and decompress functions are dropped from opclass and 
extension. Index Only Scan is enabled.

There are two more functions which can be deleted
ghstore_decompress
g_intbig_decompress
But it will not lead to any feasible consequences.


[0] 
https://www.postgresql.org/message-id/flat/CAJEAwVELVx9gYscpE%3DBe6iJxvdW5unZ_LkcAaVNSeOwvdwtD%3DA%40mail.gmail.com#CAJEAwVELVx9gYscpE=Be6iJxvdW5unZ_LkcAaVNSeOwvdwtD=a...@mail.gmail.com



 

0001-Create-cube-opclass-without-toasting.patch
Description: Binary data


0001-Enable-Index-Only-Scan-in-seg.patch
Description: Binary data

-- 
Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-hackers