Обсуждение: document json[b] limitation

Hi there,

Attached is a small patch, which documents the maximum size of
json[b] types. Probably, it's worth to patch previous releases, where
the types were introduced.

Best regards,
Oleg

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

Oleg Bartunov <obartunov@postgrespro.ru> writes:
> Attached is a small patch, which documents the maximum size of
> json[b] types. Probably, it's worth to patch previous releases, where
> the types were introduced.

If you said "maximum size is 1GB", period, I'd believe it ... although
I'm pretty sure that general limitation is already documented elsewhere.
I don't believe that it's possible to make a 256 Gb jsonb.  How will
that fit in the varlena header?

            regards, tom lane

On Wed, Apr 25, 2018 at 2:12 AM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Oleg Bartunov <obartunov@postgrespro.ru> writes:
>> Attached is a small patch, which documents the maximum size of
>> json[b] types. Probably, it's worth to patch previous releases, where
>> the types were introduced.
>
> If you said "maximum size is 1GB", period, I'd believe it ... although
> I'm pretty sure that general limitation is already documented elsewhere.
> I don't believe that it's possible to make a 256 Gb jsonb.  How will
> that fit in the varlena header?

Oops, it should be 256 Mb :)

>
>                         regards, tom lane
>



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

On Wed, Apr 25, 2018 at 6:50 PM, Oleg Bartunov <obartunov@postgrespro.ru> wrote:
> On Wed, Apr 25, 2018 at 2:12 AM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> Oleg Bartunov <obartunov@postgrespro.ru> writes:
>>> Attached is a small patch, which documents the maximum size of
>>> json[b] types. Probably, it's worth to patch previous releases, where
>>> the types were introduced.
>>
>> If you said "maximum size is 1GB", period, I'd believe it ... although
>> I'm pretty sure that general limitation is already documented elsewhere.
>> I don't believe that it's possible to make a 256 Gb jsonb.  How will
>> that fit in the varlena header?
>
> Oops, it should be 256 Mb :)

patch attached.

>
>>
>>                         regards, tom lane
>>
>
>
>
> --
> Postgres Professional: http://www.postgrespro.com
> The Russian Postgres Company



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

On Wed, Apr 25, 2018 at 06:50:51PM +0300, Oleg Bartunov wrote:
> Oops, it should be 256 Mb :)

The numbers you are presenting are right, aka 1GB for json:
=# create table aa (a json);
CREATE TABLE
=# insert into aa select ('{"key":"' || repeat('a', 512 * 1024 * 1024) ||
     repeat('a', 500 * 1024 * 1024) || '"}')::json;
INSERT 0 1
=# insert into aa select ('{"key":"' || repeat('a', 512 * 1024 *
     1024) || repeat('a', 512 * 1024 * 1024) || '"}')::json;
ERROR:  XX000: invalid memory alloc request size 1073741836
LOCATION:  palloc, mcxt.c:934

And 256MB for jsonb:
=# create table ab (a jsonb);
CREATE TABLE
=# insert into aa select ('{"key":"' || repeat('a', 256 * 1024 *
1024) || '"}')::jsonb;
ERROR:  54000: string too long to represent as jsonb string
DETAIL:  Due to an implementation restriction, jsonb strings cannot
exceed 268435455 bytes.

Be sure to use an upper-case "B" to mean bytes and not bits in the
documentation.
--
Michael