I've renamed maxmemoryToString to evictPolicyToString since that is
more accurate (and easier to mentally connect with the correct data), as
well as updated the function to user server.maxmemory_policy rather than
server.maxmemory. Now with a default config it is actually returning
the correct policy rather than volatile-lru.
The new bitfield command is an extension to the Redis bit operations,
where not just single bit operations are performed, but the array of
bits composing a string, can be addressed at random, not aligned
offsets, with any width unsigned and signed integers like u8, s5, u10
(up to 64 bit signed integers and 63 bit unsigned integers).
The BITFIELD command supports subcommands that can SET, GET, or INCRBY
those arbitrary bit counters, with multiple overflow semantics.
Trivial and credits:
A similar command was imagined a few times in the past, but for
some reason looked a bit far fetched or not well specified.
Finally the command was proposed again in a clear form by
Yoav Steinberg from Redis Labs, that proposed a set of commands on
arbitrary sized integers stored at bit offsets.
Starting from this proposal I wrote an initial specification of a single
command with sub-commands similar to what Yoav envisioned, using short
names for types definitions, and adding control on the overflow.
This commit is the resulting implementation.
Examples:
BITFIELD mykey OVERFLOW wrap INCRBY i2 10 -1 GET i2 10
An exposed Redis instance on the internet can be cause of serious
issues. Since Redis, by default, binds to all the interfaces, it is easy
to forget an instance without any protection layer, for error.
Protected mode try to address this feature in a soft way, providing a
layer of protection, but giving clues to Redis users about why the
server is not accepting connections.
When protected mode is enabeld (the default), and if there are no
minumum hints about the fact the server is properly configured (no
"bind" directive is used in order to restrict the server to certain
interfaces, nor a password is set), clients connecting from external
intefaces are refused with an error explaining what to do in order to
fix the issue.
Clients connecting from the IPv4 and IPv6 lookback interfaces are still
accepted normally, similarly Unix domain socket connections are not
restricted in any way.
The old test, designed to do a transformation on the bits that was
invertible, in order to avoid touching the original memory content, was
not effective as it was redis-server --test-memory. The former often
reported OK while the latter was able to spot the error.
So the test was substituted with one that may perform better, however
the new one must backup the memory tested, so it tests memory in small
pieces. This limits the effectiveness because of the CPU caches. However
some attempt is made in order to trash the CPU cache between the fill
and the check stages, but not for the addressing test unfortunately.
We'll see if this test will be able to find errors where the old failed.
Currently this feature is only accessible via DEBUG for testing, since
otherwise depending on the instance configuration a given script works
or is broken, which is against the Redis philosophy.
By calling redis.replicate_commands(), the scripting engine of Redis
switches to commands replication instead of replicating whole scripts.
This is useful when the script execution is costly but only results in a
few writes performed to the dataset.
Morover, in this mode, it is possible to call functions with side
effects freely, since the script execution does not need to be
deterministic: anyway we'll capture the outcome from the point of view
of changes to the dataset.
In this mode math.random() returns different sequences at every call.
If redis.replicate_commnads() is not called before any other write, the
command returns false and sticks to whole scripts replication instead.
Sometimes it can be useful for clients to completely disable replies
from the Redis server. For example when the client sends fire and forget
commands or performs a mass loading of data, or in caching contexts
where new data is streamed constantly. In such contexts to use server
time and bandwidth in order to send back replies to clients, which are
going to be ignored, is a shame.
Multiple mechanisms are possible to implement such a feature. For
example it could be a feature of MULTI/EXEC, or a command prefix
such as "NOREPLY SADD myset foo", or a different mechanism that allows
to switch on/off requests using the CLIENT command.
The MULTI/EXEC approach has the problem that transactions are not
strictly part of the no-reply semantics, and if we want to insert a lot
of data in a bulk way, creating a huge MULTI/EXEC transaction in the
server memory is bad.
The prefix is the best in this specific use case since it does not allow
desynchronizations, and is pretty clear semantically. However Redis
internals and client libraries are not prepared to handle this
currently.
So the implementation uses the CLIENT command, providing a new REPLY
subcommand with three options:
CLIENT REPLY OFF disables the replies, and does not reply itself.
CLIENT REPLY ON re-enables the replies, replying +OK.
CLIENT REPLY SKIP only discards the reply of the next command, and
like OFF does not reply anything itself.
The reason to add the SKIP command is that it allows to have an easy
way to send conceptually "single" commands that don't need a reply
as the sum of two pipelined commands:
CLIENT REPLY SKIP
SET key value
Note that CLIENT REPLY ON replies with +OK so it should be used when
sending multiple commands that don't need a reply. However since it
replies with +OK the client can check that the connection is still
active and all the previous commands were received.
This is currently just into Redis "unstable" so the proposal can be
modified or abandoned based on users inputs.
This new function is able to restart the server "in place". The current
Redis process executes the same executable it was executed with, using
the same arguments and configuration file.
After the introduction of the list with clients with pending writes, to
process clients incrementally outside of the event loop we also need to
process the pending writes list.
