This patch improves EC GET response handling:
- The proxy no longer requires all object servers to have a
durable file for the fragment archive that they return in
response to a GET. The proxy will now be satisfied if just
one object server has a durable file at the same timestamp
as fragments from other object servers.
This means that the proxy can now successfully GET an
object that had missing durable files when it was PUT.
- The proxy will now ensure that it has a quorum of *unique*
fragment indexes from object servers before considering a
GET to be successful.
- The proxy is now able to fetch multiple fragment archives
having different indexes from the same node. This enables
the proxy to successfully GET an object that has some
fragments that have landed on the same node, for example
after a rebalance.
This new behavior is facilitated by an exchange of new
headers on a GET request and response between the proxy and
object servers.
An object server now includes with a GET (or HEAD) response:
- X-Backend-Fragments: the value of this describes all
fragment archive indexes that the server has for the
object by encoding a map of the form: timestamp -> <list
of fragment indexes>
- X-Backend-Durable-Timestamp: the value of this is the
internal form of the timestamp of the newest durable file
that was found, if any.
- X-Backend-Data-Timestamp: the value of this is the
internal form of the timestamp of the data file that was
used to construct the diskfile.
A proxy server now includes with a GET request:
- X-Backend-Fragment-Preferences: the value of this
describes the proxy's current preference with respect to
those fragments that it would have object servers
return. It encodes a list of timestamp, and for each
timestamp a list of fragment indexes that the proxy does
NOT require (because it already has them).
The presence of a X-Backend-Fragment-Preferences header
(even one with an empty list as its value) will cause the
object server to search for the most appropriate fragment
to return, disregarding the existence or not of any
durable file. The object server assumes that the proxy
knows best.
Closes-Bug: 1469094
Closes-Bug: 1484598
Change-Id: I2310981fd1c4622ff5d1a739cbcc59637ffe3fc3
Co-Authored-By: Paul Luse <paul.e.luse@intel.com>
Co-Authored-By: Clay Gerrard <clay.gerrard@gmail.com>
44a861787a