Track bandwidth used by clients and replication (but diskless
replication is not tracked since the actual transfer happens in the
child process).
This includes a refactoring that makes tracking new instantaneous
metrics simpler.
PFCOUNT is technically speaking a write command, since the cached value
of the HLL is exposed in the data structure (design error, mea culpa), and
can be modified by PFCOUNT.
However if we flag PFCOUNT as "w", read only slaves can't execute the
command, which is a problem since there are environments where slaves
are used to scale PFCOUNT reads.
Nor it is possible to just prevent PFCOUNT to modify the data structure
in slaves, since without the cache we lose too much efficiency.
So while this commit allows slaves to create a temporary inconsistency
(the strings representing the HLLs in the master and slave can be
different in certain moments) it is actually harmless.
In the long run this should be probably fixed by turning the HLL into a
more opaque representation, for example by storing the cached value in
the part of the string which is not exposed (this should be possible
with SDS strings).
start_server now uses return value from Tcl exec to get the server pid,
however this introduces errors that depend from timing: a lot of the
testing code base assumed the server to be actually up and running when
server_start returns.
So the old code that waits to see the pid in the log file was restored.
bulk_data field size was not removed from the count. It is not possible
to declare it simply as 'char bulk_data[]' since the structure is nested
into another structure.
Because of (not so) recent Redis changes, now the LRU internally
reported unit is milliseconds, not seconds, but the DEBUG OBJECT output
was still claiming seconds while providing milliseconds.
However OBJECT IDLETIME was working as expected, which is the correct
API to use.
zmalloc(0) cauesd to actually trigger a non-zero allocation since with
standard libc malloc we have our own zmalloc header for memory tracking,
but at the same time the returned pointer is at the end of the block and
not in the middle. This triggers a false positive when testing with
valgrind.
When the inline protocol args count is 0, we now avoid reallocating
c->argv, preventing the issue to happen.
