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
This commit fixes two corner cases for the TTL command.
1) When the key was already logically expired (expire time older
than current time) the command returned -1 instead of -2.
2) When the key was existing and the expire was found to be exactly 0
(the key was just about to expire), the command reported -1 (that is, no
expire) instead of a TTL of zero (that is, about to expire).
MULTI/EXEC is now propagated to the AOF / Slaves only once we encounter
the first command that is not a read-only one inside the transaction.
The old behavior was to always propagate an empty MULTI/EXEC block when
the transaction was composed just of read only commands, or even
completely empty. This created two problems:
1) It's a bandwidth waste in the replication link and a space waste
inside the AOF file.
2) We used to always increment server.dirty to force the propagation of
the EXEC command, resulting into triggering RDB saves more often
than needed.
Note: even read-only commands may also trigger writes that will be
propagated, when we access a key that is found expired and Redis will
synthesize a DEL operation. However there is no need for this to stay
inside the transaction itself, but only to be ordered.
So for instance something like:
MULTI
GET foo
SET key zap
EXEC
May be propagated into:
DEL foo
MULTI
SET key zap
EXEC
While the DEL is outside the transaction, the commands are delivered in
the right order and it is not possible for other commands to be inserted
between DEL and MULTI.
Redis-tools is a connection of tools no longer mantained that was
intented as a way to economically make sense of Redis in the pre-vmware
sponsorship era. However there was a nice redis-stat utility, this
commit imports one of the functionalities of this tool here in redis-cli
as it seems to be pretty useful.
Usage: redis-cli --stat
The output is similar to vmstat in the format, but with Redis specific
stuff of course.
From the point of view of the monitored instance, only INFO is used in
order to grab data.
This is needed in order to colorize it as next step.
We use conventions in output messages such as
>>> This is an action
*** This is a warning
[ERR] This is an error
[OK] That's fine
And so forth, so that a color will be associated checking the first
three chars.
When a master turns into a slave after a failover event, make sure to
clear the assigned slots before setting up the replication, as a slave
should never claim slots in an explicit way, but just take over the
master slots when replacing its master.
A slave node set this flag for itself when, after receiving authorization
from the majority of nodes, it turns itself into a master.
At the same time now this flag is tested by nodes receiving a PING
message before reconfiguring after a failover event. This makes the
system more robust: even if currently there is no way to manually turn
a slave into a master it is possible that we'll have such a feature in
the future, or that simply because of misconfiguration a node joins the
cluster as master while others believe it's a slave. This alone is now
no longer enough to trigger reconfiguration as other nodes will check
for the PROMOTED flag.
The PROMOTED flag is cleared every time the node is turned back into a
replica of some other node.
Sender flags were not propagated for the sender, but only for nodes in
the gossip section. This is odd and in the next commits we'll need to
get updated flags for the sender node, so this commit adds a new field
in the cluster messages header.
The message header is the same size as we reused some free space that
was marked as 'unused' because of alignment concerns.
So when the failing master node is back in touch with the cluster,
instead of remaining unused it is converted into a replica of the
new master, ready to perform the fail over if the new master node
will fail at some point.
Note that as a side effect clients with stale configuration are now
not an issue as well, as the node converted into a slave will not
accept queries but will redirect clients accordingly.
The code handling a master that turns into a slave or the contrary was
improved in order to avoid repeating the same operations. Also
the readability and conceptual simplicity was improved.
