Re: Sequence Access Method WIP

The following review has been posted through the commitfest application:
make installcheck-world:  not tested
Implements feature:       not tested
Spec compliant:           not tested
Documentation:            not tested

[Partial review] Evaluated: 0002-gapless-seq-2016-03-29-2.patch
Needs updating code copyright years ... or is this really from 2013? [ contrib/gapless_seq/gapless_seq.c ]
Patch applies cleanly to current master (3063e7a84026ced2aadd2262f75eebbe6240f85b)
It does compile cleanly.

DESIGN
The decision to hardcode the schema GAPLESS_SEQ_NAMESPACE ("gapless_seq") and VALUES_TABLE_NAME ("seqam_gapless_values") strikes me a bit: while I understand the creation of a private schema named after the extension, it seems overkill for just a single table.
I would suggest to devote some reserved schema name for internal implementation details and/or AM implementation details, if deemed reasonable.
On the other hand, creating the schema/table upon extension installation makes the values table use the default tablespace for the database, which can be good for concurrency --- direct writes to less loaded storage
   (Note that users may want to move this table into an SSD-backed tablespace or equivalently fast storage ... moreso when many --not just one-- gapless sequences are being used)

Yet, there is <20141203102425.GT2456@alap3.anarazel.de> where Andres argues against anything different than one-page-per-sequence implementations.
   I guess this patch changes everything in this respect.

CODE
  seqam_gapless_init(Relation seqrel, Form_pg_sequence seq, int64 restart_value,
                                bool restart_requested, bool is_init)
  -> is_init sounds confusing; suggest renaming to "initialize" or "initial" to avoid reading as "is_initIALIZED"

DEPENDS ON 0001-seqam-v10.patch , which isn't commited yet --- and it doesn't apply cleanly to current git master.
Please update/rebase the patch and resubmit.