We need to remember what is the saving strategy of the current RDB child
process, since the configuration may be modified at runtime via CONFIG
SET and still we'll need to understand, when the child exists, what to
do and for what goal the process was initiated: to create an RDB file
on disk or to write stuff directly to slave's sockets.

However we don't try to do this if the integer is already inside a range
representable with a shared integer.

The performance gain appears to be around ~15% in micro benchmarks,
however in the long run this also helps to improve locality, so should
have more, hard to measure, benefits.

Closes #2029

Closes #2002

Closes #1960

Closes #1938

Some language in the comment was difficult
to understand, so this commit: clarifies wording, removes
unnecessary words, and relocates some dependent clauses
closer to what they actually describe.

I also tried to break up longer chains of thought
(if X, then Y, and Q, and also F, so obviously M)
into more manageable chunks for ease of understanding.

Closes #1523

  - Remove trailing newlines from redis.conf
  - Fix comment misspelling
  - Clarifies zipEncodeLength usage and a C API mention (#1243, #1242)
  - Fix cluster typos (inspired by @papanikge #1507)
  - Fix rewite -> rewrite in a few places (inspired by #682)

Closes #1243, #1242, #1507

Closes #1351

Closes #1373

Closes #1386

Closes #1513

Closes #1537

Closes #1682

error != success; and 0 != number of bytes written

Closes #1806

Closes #1871

Closes #1877

The old DEBUG POPULATE form for automatic creation of test keys is:

    DEBUG POPULATE <count>

Now an additional form is available:

    DEBUG POPULATE <count> <prefix>

When prefix is not specified, it defaults to "key", so the keys are
named incrementally from key:0 to key:<count-1>. Otherwise the specified
prefix is used instead of "key".

The command is useful in order to populate different Redis instances
with key names guaranteed to don't collide. There are other debugging
uses, for example it is possible to add additional N keys using a count
of N and a random prefix at every call.

Following the CLIENT LIST output format, we prefix the unix socket
address with a "/" so that it is different than an IPv4/6 address.
This makes parsing simpler.

Related to #2010.

Related to PR #2010.

This fixes a potential bug that was never observed in practice since
what happens is that the asynchronous connect returns ok (to fail later,
calling the handler) every time, so a ping is queued, and sent_ping
happens to always be populated.

Howver technically connect(2) with a non blocking socket may return an
error synchronously, so before this fix the code was not correct.

It is not clear if files open in append only mode will automatically fix
their offset after a truncate(2) operation. This commit makes sure that
we reposition the AOF file descriptor offset at the end of the file
after a truncated AOF is loaded and trimmed to the last valid command.

Recently we introduced the ability to load truncated AOFs, but
unfortuantely the support was broken since the server, after loading the
truncated AOF, continues appending to the file that is corrupted at the
end. The problem is fixed only in the next AOF rewrite.

This commit fixes the issue by truncating the AOF to the last valid
opcode, and aborting if it is not possible to truncate the file
correctly.

This is a general fix (check that dirty delta is positive) but actually
should have as the only effect fixing the SAVE propagation to
AOF and slaves.

The code to check the number of voters was never updated to follow the new
Sentinel specification, so the number of voters was computed using only
the set of Sentinels that provided a vote.

This means that there is a changing majority on partitions, even if
usually the issue is not triggered because of the configured quorum
check (what was broken was the other implicit check that requires anyway
half of the known sentinels to agree in order to start a failover).

As discussed in issue #1945.

*SCAN will cause redis server to hang for seconds
after millions of keys was deleted by SCAN/DEL pairs