Change 23266

C. Thomas Tyler
Fixes and Enhancements:
* Enabled operate on edge servers, to
keep /p4/N/offline_db current on those hosts for site-local
recovery w/o requiring a site-local replica (though having
a site-local replica can still be useful).
* Disabled for edge servers.
* More fully support topologies using edge severs, in both
geographically distributed and horizaontal scaling "wokspace
server" solutions.
* Fix broken EDGESERVER value definition.
* Modified name of SDP counter that gets set when a checkpoint is taken
to incorporate ServerID, so now the counter name will look like
lastSDPCheckpoint.master.1, or lastSDPCheckpoint.p4d_edge_sfo, rather
than just lastSDPCheckpoint.

There will be multiple such counters in a topology that uses edge
servers, and/or which takes checkpoints on replicas.

* Added comments for all functions.

For the master server, journalPrefix remains:

The /p4/N/checkpoints is reserved for writing by the
master/commit server only.

For non-standby (possibly filtered) replicas and edge serves,
journalPrefix is:

Here, ShortServerID is just the ServerID with the 'p4d_' prefix
trimmed, since it is redundant in this context.  See,
which enshines a ServerID (server spec) naming standard, with
values like 'p4d_fr_bos' (forwarding replica in Boston) and
p4d_edge_blr (Edge server in Bangalore).  So the journalPrefix
for the p4d_edge_bos replica would be:

For "standby" (aka journalcopy) replicas, journalPrefix is set
to /p4/N/journals.rep. which is written to the $LOGS volume, due
to the nature of standby replicas using journalPrefix to write
active server logs to pre-rotated journals.

Some take-away to be updated in docs:
* The /p4/N/checkpoints folder must be reserved for checkpoints that
originate on the master. It should be safe to rsync this folder
(with --delete if desired) to any replica or edge server.  This is
consistent with the current SDP.
* I want to change 'journals.rep' to 'checkpoints.<ShortServerID>'
for non-standby replicas, to ensure that checkpoints and journals
taken on those hosts are written to a volume where they are backed
* In sites with multiple edge serves, some sharing achive files
('workspace servers'), multiple edge servers will share the same
SAN. So we one checkpoints dir per ServerID, and we want that
dir to be on the /hxdepots volume.

Note that the journalPrefix for replicas was a fixed /p4/N/journals.rep.
This was on the /hxlogs volume - a presumably fast-for-writes volume,
but typically NOT backed up and not very large. This change puts it
under /p4/N/checkpoints.* for edge servers and non-standby replicas,
but ensures other replica types and edge servers can generate
checkpoints to a location that is backed up and has plenty of storage
capacity.  For standby replicas only (which cannot be filtered),
the journalPrefix remains /p4/N/journals.rep on the /hxlogs volume.
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