The API is one of the bulding blocks of CLUSTER FAILOVER command that
executes a manual failover in Redis Cluster. However exposed as a
command that the user can call directly, it makes much simpler to
upgrade a standalone Redis instance using a slave in a safer way.
The commands works like that:
CLIENT PAUSE <milliesconds>
All the clients that are not slaves and not in MONITOR state are paused
for the specified number of milliesconds. This means that slaves are
normally served in the meantime.
At the end of the specified amount of time all the clients are unblocked
and will continue operations normally. This command has no effects on
the population of the slow log, since clients are not blocked in the
middle of operations but only when there is to process new data.
Note that while the clients are unblocked, still new commands are
accepted and queued in the client buffer, so clients will likely not
block while writing to the server while the pause is active.
In high RPS environments, the default listen backlog is not sufficient, so
giving users the power to configure it is the right approach, especially
since it requires only minor modifications to the code.
A client can enter a special cluster read-only mode using the READONLY
command: if the client read from a slave instance after this command,
for slots that are actually served by the instance's master, the queries
will be processed without redirection, allowing clients to read from
slaves (but without any kind fo read-after-write guarantee).
The READWRITE command can be used in order to exit the readonly state.
When a slave was disconnected from its master the replication offset was
reported as -1. Now it is reported as the replication offset of the
previous master, so that failover can be performed using this value in
order to try to select a slave with more processed data from a set of
slaves of the old master.
During the refactoring of blocking operations, commit
82b672f633, a bug was introduced where
a milliseconds time is compared to a seconds time, so all the clients
always appear to timeout if timeout is set to non-zero value.
Thanks to Jonathan Leibiusky for finding the bug and helping verifying
the cause and fix.
Some are just to know if the master is down, and in this case the runid
in the request is set to "*", others are actually in order to seek for a
vote and get elected. In the latter case the runid is set to the runid
of the instance seeking for the vote.
All the internal state of cluster involving time is now using mstime_t
and mstime() in order to use milliseconds resolution.
Also the clusterCron() function is called with a 10 hz frequency instead
of 1 hz.
The cluster node_timeout must be also configured in milliseconds by the
user in redis.conf.
Example:
db0:keys=221913,expires=221913,avg_ttl=655
The algorithm uses a running average with only two samples (current and
previous). Keys found to be expired are considered at TTL zero even if
the actual TTL can be negative.
The TTL is reported in milliseconds.
We don't want to repeat a fast cycle too soon, the previous code was
broken, we need to wait two times the period *since* the start of the
previous cycle in order to avoid there is an even space between cycles:
.-> start .-> second start
| |
+-------------+-------------+--------------+
| first cycle | pause | second cycle |
+-------------+-------------+--------------+
The second and first start must be PERIOD*2 useconds apart hence the *2
in the new code.
This commit makes the fast collection cycle time configurable, at
the same time it does not allow to run a new fast collection cycle
for the same amount of time as the max duration of the fast
collection cycle.
The main idea here is that when we are no longer to expire keys at the
rate the are created, we can't block more in the normal expire cycle as
this would result in too big latency spikes.
For this reason the commit introduces a "fast" expire cycle that does
not run for more than 1 millisecond but is called in the beforeSleep()
hook of the event loop, so much more often, and with a frequency bound
to the frequency of executed commnads.
The fast expire cycle is only called when the standard expiration
algorithm runs out of time, that is, consumed more than
REDIS_EXPIRELOOKUPS_TIME_PERC of CPU in a given cycle without being able
to take the number of already expired keys that are yet not collected
to a number smaller than 25% of the number of keys.
You can test this commit with different loads, but a simple way is to
use the following:
Extreme load with pipelining:
redis-benchmark -r 100000000 -n 100000000 \
-P 32 set ele:rand:000000000000 foo ex 2
Remove the -P32 in order to avoid the pipelining for a more real-world
load.
In another terminal tab you can monitor the Redis behavior with:
redis-cli -i 0.1 -r -1 info keyspace
and
redis-cli --latency-history
Note: this commit will make Redis printing a lot of debug messages, it
is not a good idea to use it in production.
Previously two string encodings were used for string objects:
1) REDIS_ENCODING_RAW: a string object with obj->ptr pointing to an sds
stirng.
2) REDIS_ENCODING_INT: a string object where the obj->ptr void pointer
is casted to a long.
This commit introduces a experimental new encoding called
REDIS_ENCODING_EMBSTR that implements an object represented by an sds
string that is not modifiable but allocated in the same memory chunk as
the robj structure itself.
The chunk looks like the following:
+--------------+-----------+------------+--------+----+
| robj data... | robj->ptr | sds header | string | \0 |
+--------------+-----+-----+------------+--------+----+
| ^
+-----------------------+
The robj->ptr points to the contiguous sds string data, so the object
can be manipulated with the same functions used to manipulate plan
string objects, however we need just on malloc and one free in order to
allocate or release this kind of objects. Moreover it has better cache
locality.
This new allocation strategy should benefit both the memory usage and
the performances. A performance gain between 60 and 70% was observed
during micro-benchmarks, however there is more work to do to evaluate
the performance impact and the memory usage behavior.
This code is only responsible to take an LRU-evicted fixed length cache
of SHA1 that we are sure all the slaves received.
In this commit only the implementation is provided, but the Redis core
does not use it to actually send EVALSHA to slaves when possible.
The old REDIS_CMD_FORCE_REPLICATION flag was removed from the
implementation of Redis, now there is a new API to force specific
executions of a command to be propagated to AOF / Replication link:
void forceCommandPropagation(int flags);
The new API is also compatible with Lua scripting, so a script that will
execute commands that are forced to be propagated, will also be
propagated itself accordingly even if no change to data is operated.
As a side effect, this new design fixes the issue with scripts not able
to propagate PUBLISH to slaves (issue #873).
Currently it implements three subcommands:
PUBSUB CHANNELS [<pattern>] List channels with non-zero subscribers.
PUBSUB NUMSUB [channel_1 ...] List number of subscribers for channels.
PUBSUB NUMPAT Return number of subscribed patterns.
This feature allows the user to specify the minimum number of
connected replicas having a lag less or equal than the specified
amount of seconds for writes to be accepted.
There is a new 'lag' information in the list of slaves, in the
"replication" section of the INFO output.
Also the format was changed in a backward incompatible way in order to
make it more easy to parse if new fields are added in the future, as the
new format is comma separated but has named fields (no longer positional
fields).
Also the logfile option was modified to always have an explicit value
and to log to stdout when an empty string is used as log file.
Previously there was special handling of the string "stdout" that set
the logfile to NULL, this always required some special handling.
When a BGSAVE fails, Redis used to flood itself trying to BGSAVE at
every next cron call, that is either 10 or 100 times per second
depending on configuration and server version.
This commit does not allow a new automatic BGSAVE attempt to be
performed before a few seconds delay (currently 5).
This avoids both the auto-flood problem and filling the disk with
logs at a serious rate.
The five seconds limit, considering a log entry of 200 bytes, will use
less than 4 MB of disk space per day that is reasonable, the sysadmin
should notice before of catastrofic events especially since by default
Redis will stop serving write queries after the first failed BGSAVE.
This fixes issue #849
server.repl_down_since used to be initialized to the current time at
startup. This is wrong since the replication never started. Clients
testing this filed to check if data is uptodate should never believe
data is recent if we never ever connected to our master.
This fixes cases where the RDB file does exist but can't be accessed for
any reason. For instance, when the Redis process doesn't have enough
permissions on the file.
activeExpireCycle() tries to test just a few DBs per iteration so that
it scales if there are many configured DBs in the Redis instance.
However this commit makes it a bit smarter when one a few of those DBs
are under expiration pressure and there are many many keys to expire.
What we do is to remember if in the last iteration had to return because
we ran out of time. In that case the next iteration we'll test all the
configured DBs so that we are sure we'll test again the DB under
pressure.
Before of this commit after some mass-expire in a given DB the function
tested just a few of the next DBs, possibly empty, a few per iteration,
so it took a long time for the function to reach again the DB under
pressure. This resulted in a lot of memory being used by already expired
keys and never accessed by clients.
This small number of DBs is set to 16 so actually in the default
configuraiton Redis should behave exactly like in the past.
However the difference is that when the user configures a very large
number of DBs we don't do an O(N) operation, consuming a non trivial
amount of CPU per serverCron() iteration.
This is the first step to lower the CPU usage when many databases are
configured. The other is to also process a limited number of DBs per
call in the active expire cycle.
A new server.orig_commands table was added to the server structure, this
contains a copy of the commant table unaffected by rename-command
statements in redis.conf.
A new API lookupCommandOrOriginal() was added that checks both tables,
new first, old later, so that rewriteClientCommandVector() and friends
can lookup commands with their new or original name in order to fix the
client->cmd pointer when the argument vector is renamed.
This fixes the segfault of issue #986, but does not fix a wider range of
problems resulting from renaming commands that actually operate on data
and are registered into the AOF file or propagated to slaves... That is
command renaming should be handled with care.
