On Tue, Apr 26, 2016 at 6:40 AM, Tom Lane <t...@sss.pgh.pa.us> wrote:
> Craig Ringer <cr...@2ndquadrant.com> writes:
>> On 26 April 2016 at 14:06, 陈天舟 <tianzhouc...@gmail.com> wrote:
>>> (1) Since each protocol buffer column requires a schema. I am not sure
>>> where is the best place to store that schema info. Should it be in a
>>> CONSTRAINT (but I am not able to find the doc referring any custom
>>> constraint), or should it be in the COMMENT or somewhere else?
>> I can't really imagine how you'd do that without adding a new catalog like
>> we have for enum members. A typmod isn't sufficient since you need a whole
>> lot more than an integer, and typmods aren't tracked throughout the server
>> that well.
>> That'll make it hard to do it with an extension.
> PostGIS manages to reference quite a lot of schema-like information via
> a geometry column's typmod. Maybe there's a reason why their approach
> wouldn't be a good fit for this, but it'd be worth investigating.
We pack a short type number, two flags and 24 bits of SRID number into
an integer. The SRID number is in turn a foreign key into the
spatial_ref_sys table where the fully spelled out spatial reference
definition lives. It's not very nice, and it's quite breakable since
there's no foreign key integrity between the typmod and the
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