Re: Maximum number of columns in a table

[Martin Gainty <mgainty@xxxxxxxxxxx>]

*guess i'm not used to seeing such thoughtful responses*

please keep us all apprised on how your implementation progresses!

Martin
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> From: gerry@xxxxxxxxxx
> To: sam@xxxxxxxxxxxxx; tgl@xxxxxxxxxxxxx
> CC: pgsql-general@xxxxxxxxxxxxxx
> Subject: Re: Maximum number of columns in a table
> Date: Sun, 12 Apr 2009 09:52:29 +1000
>
> Thank you gentlemen. I believe I am now enlightened.
>
> 1. The maximum number of rows per table is not limited by an algorithm at
> CREATE/ALTER TABLE other than to enforce an absolute maximum number of
> columns of 1600.
>
> 2. The ability to store any individual row depends on its content.
>
> I hasten to add that I am simply catering for a boundary condition which
> would (surely) never occur but I have to be defensive here. My aim is simply
> to cover this without unduly impacting the normal case.
>
> I have been researching this for some time and I am truly grateful for your
> expert and thoughtful assistance.
>
> Gerry
>
> ----- Original Message -----
> From: "Tom Lane" <tgl@xxxxxxxxxxxxx>
> To: "Sam Mason" <sam@xxxxxxxxxxxxx>
> Cc: <pgsql-general@xxxxxxxxxxxxxx>
> Sent: Sunday, April 12, 2009 9:26 AM
> Subject: Re: [GENERAL] Maximum number of columns in a table
>
>
> > Sam Mason <sam@xxxxxxxxxxxxx> writes:
> >> Just out of interest; what would happen if you had:
> >
> >> CREATE TABLE wider (
> >> col0001 TEXT,
> >> col0002 TEXT,
> >> -- [ .... ]
> >> col9998 TEXT,
> >> col9999 TEXT
> >> );
> >
> >> CREATE TABLE store (
> >> pk1 INTEGER,
> >> pk2 TEXT,
> >> PRIMARY KEY (pk1,pk2),
> >> data wider
> >> );
> >
> >> Would the "data" tend to end up toasted, or would PG try and expand the
> >> data inline and fail some of the time?
> >
> > The toast code doesn't recurse into composite values. It would see the
> > "data" column as one single value, so most of the time data would get
> > toasted and pushed out as a unit. You probably don't want to adopt the
> > above design. (Also, you'd still be subject to the 1600 column limit
> > on the number of fields within "data", because that comes from a tuple
> > header field width limit that has nothing to do with total tuple size.)
> >
> >> Also, if I ran the following query:
> >
> >> SELECT pk1, pk2, (data).col0001, (data).col0101 FROM store;
> >
> >> Would "data" get detoasted once per row, or per column referenced?
> >
> > Probably the latter. I did some work a few months ago trying to make
> > the former happen, but it crashed and burned for reasons I don't recall
> > at the moment.
> >
> > regards, tom lane
> >
> > --
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>
>
> --
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