The PING trigger was improved again by using two fields instead of a
single one to remember when the last ping was sent:
1. The "active" ping is the time at which we sent the last ping that
still received no reply. However we continue to ping non replying
instances even if they have an old active ping: the link may be
disconnected and reconencted in the meantime so the older pings may get
lost even if it's a TCP socket.
2. The "last" ping is the time at which we really sent the last ping
on the wire, and this is used in order to throttle the amount of pings
we send during failures (when no pong is received).
All in all the failure detector effectiveness should be identical but we
avoid to flood instances with pings during failures or when they are
slow.
It's ok to ping as soon as the ping period has elapsed since we received
the last PONG, but it's not good that we ping again if there is a
pending ping... With this change we'll send a new ping if there is one
pending only if two times the ping period elapsed since the ping which
is still pending was sent.
This is useful for debugging and logging activities: given a
sentinelRedisInstance object returns a C string representing the
instance type: master, slave, sentinel.
This new command triggers a config flush to save the in-memory config to
disk. This is useful for cases of a configuration management system or a
package manager wiping out your sentinel config while the process is
still running - and has not yet been restarted. It can also be useful
for scripting a backup and migrate or clone of a running sentinel.
Since with a previous commit Sentinels now persist their unique ID, we
no longer need to detect duplicated Sentinels and re-add them. We remove
and re-add back using different events only in the case of address
switch of the same Sentinel, without generating a new +sentinel event.
Previously Sentinels always changed unique ID across restarts, relying
on the server.runid field. This is not a good idea, and forced Sentinel
to rely on detection of duplicated Sentinels and a potentially dangerous
clean-up and re-add operation of the Sentinel instance that was
rebooted.
Now the ID is generated at the first start and persisted in the
configuration file, so that a given Sentinel will have its unique
ID forever (unless the configuration is manually deleted or there is a
filesystem corruption).
Originally, only the +slave event which occurs when a slave is
reconfigured during sentinelResetMasterAndChangeAddress triggers a flush
of the config to disk. However, newly discovered slaves don't
apparently trigger this flush but do trigger the +slave event issuance.
So if you start up a sentinel, add a master, then add a slave to the
master (as a way to reproduce it) you'll see the +slave event issued,
but the sentinel config won't be updated with the known-slave entry.
This change makes sentinel do the flush of the config if a new slave is
deteted in sentinelRefreshInstanceInfo.
To rewrite the config in the loop that adds slaves back after a master
reset, in order to handle switching to another master, is useless: it
just adds latency since there is an fsync call in the inner loop,
without providing any additional guarantee, but the contrary, since if
after the first loop iteration the server crashes we end with just a
single slave entry losing all the other informations.
It is wiser to rewrite the config at the end when the full new
state is configured.
When we fail to setup the write handler it does not make sense to take
the client around, it is missing writes: whatever is a client or a slave
anyway the connection should terminated ASAP.
Moreover what the function does exactly with its return value, and in
which case the write handler is installed on the socket, was not clear,
so the functions comment are improved to make the goals of the function
more obvious.
Also related to #2485.
master was closing the connection if the RDB transfer took long time.
and also sent PINGs to the slave before it got the initial ACK, in which case the slave wouldn't be able to find the EOF marker.
Segfault introduced during a refactoring / warning suppression a few
commits away. This particular call assumed that it is safe to pass NULL
to the object pointer argument when we are sure the set has a given
encoding. This can't be assumed and is now guaranteed to segfault
because of the new API of setTypeNext().
This change fixes several warnings compiling at -O3 level with GCC
4.8.2, and at the same time, in case of misuse of the API, we have the
pointer initialize to NULL or the integer initialized to the value
-123456789 which is easy to spot by naked eye.
No semantical changes since to make dict.c truly able to scale over the
32 bit table size limit, the hash function shoulds and other internals
related to hash function output should be 64 bit ready.
rehashidx is always positive in the two code paths, since the only
negative value it could have is -1 when there is no rehashing in
progress, and the condition is explicitly checked.
Bug as old as Redis and blocking operations. It's hard to trigger since
only happens on instance role switch, but the results are quite bad
since an inconsistency between master and slave is created.
How to trigger the bug is a good description of the bug itself.
1. Client does "BLPOP mylist 0" in master.
2. Master is turned into slave, that replicates from New-Master.
3. Client does "LPUSH mylist foo" in New-Master.
4. New-Master propagates write to slave.
5. Slave receives the LPUSH, the blocked client get served.
Now Master "mylist" key has "foo", Slave "mylist" key is empty.
Highlights:
* At step "2" above, the client remains attached, basically escaping any
check performed during command dispatch: read only slave, in that case.
* At step "5" the slave (that was the master), serves the blocked client
consuming a list element, which is not consumed on the master side.
This scenario is technically likely to happen during failovers, however
since Redis Sentinel already disconnects clients using the CLIENT
command when changing the role of the instance, the bug is avoided in
Sentinel deployments.
Closes#2473.
