document json[b] limitation

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