pgsql: tableam: Provide helper functions for relation sizing.

tableam: Provide helper functions for relation sizing.

Most block-based table AMs will need the exact same implementation of
the relation_size callback as the heap, and if they use a standard
page layout, they will likely need an implementation of the
relation_estimate_size callback that is very similar to that of the
heap. Rearrange to facilitate code reuse.

Patch by me, reviewed by Michael Paquier, Daniel Gustafsson, and
Álvaro Herrera.

Discussion: http://postgr.es/m/CA+TgmoZ6DBPnP1E-vRpQZUJQijJFD54F+SR_pxGiAAS-MyrigA@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/554106b1163853757b72ce14d7db5050c32bfa6a

Modified Files
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src/backend/access/heap/heapam_handler.c | 129 ++-----------------------
src/backend/access/table/tableam.c | 161 +++++++++++++++++++++++++++++++
src/include/access/tableam.h | 14 +++
3 files changed, 185 insertions(+), 119 deletions(-)