This adds a limit query parameter to GET
/allocation_candidates?limit=5&resource=VCPU:1
A 'limit' filter is added to the AllocationCandidates. If set, after
the database query has been run to create the allocation requests and
provider summaries, a slice or sample of the allocation requests is
taken to limit the results. The summaries are then filtered to only
include those in the allocation requests.
This method avoids needing to make changes to the generated SQL, the
creation of which is fairly complex, or the database tables. The amount
of data queried is still high in the extreme case, but the amount of
data sent over the wire (as JSON) is shrunk. This is a trade-off that
was discussed in the spec and the discussion surrounding its review.
If it turns out that memory use server-side is an issue we can
investigate changing the SQL.
A configuration setting, [placement]/randomize_allocation_candidates,
is added to allow deployers to declare whether they want the results
to be returned in whatever order the database chooses or a random
order. The default is "False" which is expected to preserve existing
behavior and impose a packing placement strategy.
When the config setting is combined with the limit parameter, if
"True" the limited results are a random sampling from the full
results. If "False", it is a slice from the front.
This is done as a new microversion, 1.16, with updates to docs, a reno
and adjustments to the api history doc.
Change-Id: I5f3d4f49c34fd3cd6b9d2e12b3c3c4cdcb409bec
Implements: bp allocation-candidates-limit
ff6d4560fe