Re: Global Sequences

Simon,

On 10/17/2012 10:34 AM, Simon Riggs wrote:
> IMHO an API is required for "give me the next allocation of numbers",
> essentially a bulk equivalent of nextval().

Agreed. That pretty exactly matches what I described (and what's
implemented in Postgres-R). The API then only needs to be called every N
invocations of nextval(), because otherwise nextval() can simply return
a cached number previously allocated in a single step, eliminating a lot
of the communication overhead.

You realize an API at that level doesn't allow for an implementation of
options 1 and 2? (Which I'm convinced we don't need, so that's fine with
me).

> Anything lower level is going to depend upon implementation details
> that I don't think we should expose.

Exactly. Just like we shouldn't expose other implementation details,
like writing to system catalogs or WAL.

> I'm sure there will be much commonality between 2 similar
> implementations, just as there is similar code in each index type. But
> maintaining modularity is important and ahead of us actually seeing 2
> implementations, trying to prejudge that is going to slow us all down
> and likely screw us up.

Agreed. Let me add, that modularity only serves a purpose, if the
boundaries between the modules are chosen wisely. It sounds like we are
on the same page, though.

To testify this: IMHO an API for setval() is required to invalidate all
node's caches and re-set an initial value, as a starting point for the
next bulk of numbers that nextval() will return.

currval() doesn't need to be changed or "hooked" at all, because it's a
read-only operation.

Regards

Markus Wanner