A reimplementation of blocking operation internals.
Redis provides support for blocking operations such as BLPOP or BRPOP.
This operations are identical to normal LPOP and RPOP operations as long
as there are elements in the target list, but if the list is empty they
block waiting for new data to arrive to the list.
All the clients blocked waiting for th same list are served in a FIFO
way, so the first that blocked is the first to be served when there is
more data pushed by another client into the list.
The previous implementation of blocking operations was conceived to
serve clients in the context of push operations. For for instance:
1) There is a client "A" blocked on list "foo".
2) The client "B" performs `LPUSH foo somevalue`.
3) The client "A" is served in the context of the "B" LPUSH,
synchronously.
Processing things in a synchronous way was useful as if "A" pushes a
value that is served by "B", from the point of view of the database is a
NOP (no operation) thing, that is, nothing is replicated, nothing is
written in the AOF file, and so forth.
However later we implemented two things:
1) Variadic LPUSH that could add multiple values to a list in the
context of a single call.
2) BRPOPLPUSH that was a version of BRPOP that also provided a "PUSH"
side effect when receiving data.
This forced us to make the synchronous implementation more complex. If
client "B" is waiting for data, and "A" pushes three elemnents in a
single call, we needed to propagate an LPUSH with a missing argument
in the AOF and replication link. We also needed to make sure to
replicate the LPUSH side of BRPOPLPUSH, but only if in turn did not
happened to serve another blocking client into another list ;)
This were complex but with a few of mutually recursive functions
everything worked as expected... until one day we introduced scripting
in Redis.
Basically you can't "rewrite" a script to have just a partial effect on
the replicas and AOF file if the script happened to serve a few blocked
clients.
The solution to all this problems, implemented by this commit, is to
change the way we serve blocked clients. Instead of serving the blocked
clients synchronously, in the context of the command performing the PUSH
operation, it is now an asynchronous and iterative process:
1) If a key that has clients blocked waiting for data is the subject of
a list push operation, We simply mark keys as "ready" and put it into a
queue.
2) Every command pushing stuff on lists, as a variadic LPUSH, a script,
or whatever it is, is replicated verbatim without any rewriting.
3) Every time a Redis command, a MULTI/EXEC block, or a script,
completed its execution, we run the list of keys ready to serve blocked
clients (as more data arrived), and process this list serving the
blocked clients.
4) As a result of "3" maybe more keys are ready again for other clients
(as a result of BRPOPLPUSH we may have push operations), so we iterate
back to step "3" if it's needed.
The new code has a much simpler semantics, and a simpler to understand
implementation, with the disadvantage of not being able to "optmize out"
a PUSH+BPOP as a No OP.
This commit will be tested with care before the final merge, more tests
will be added likely.
Make sure that SELECT argument is an integer or return an error.
Unfortunately we had still the lame atoi() without any error checking in
place, so "SELECT foo" would work as "SELECT 0". This was not an huge
problem per se but some people expected that DB can be strings and not
just numbers, and without errors you get the feeling that they can be
numbers, but not the behavior.
Now getLongFromObjectOrReply() is used as almost everybody else across
the code, generating an error if the number is not an integer or
overflows the long type.
Thanks to @mipearson for reporting that on Twitter.
remove unsafe and unnecessary cast.
until now, this cast may lead segmentation fault when end > UINT_MAX
setbit foo 0 1
bitcount 0 4294967295
=> ok
bitcount 0 4294967296
=> cause segmentation fault.
Note by @antirez: the commit was modified a bit to also change the
string length type to long, since it's guaranteed to be at max 512 MB in
size, so we can work with the same type across all the code path.
Scripting: Force SORT BY constant determinism inside SORT itself.
SORT is able to return (faster than when ordering) unordered output if
the "BY" clause is used with a constant value. However we try to play
well with scripting requirements of determinism providing always sorted
outputs when SORT (and other similar commands) are called by Lua
scripts.
However we used the general mechanism in place in scripting in order to
reorder SORT output, that is, if the command has the "S" flag set, the
Lua scripting engine will take an additional step when converting a
multi bulk reply to Lua value, calling a Lua sorting function.
This is suboptimal as we can do it faster inside SORT itself.
This is also broken as issue #545 shows us: basically when SORT is used
with a constant BY, and additionally also GET is used, the Lua scripting
engine was trying to order the output as a flat array, while it was
actually a list of key-value pairs.
What we do know is to recognized if the caller of SORT is the Lua client
(since we can check this using the REDIS_LUA_CLIENT flag). If so, and if
a "don't sort" condition is triggered by the BY option with a constant
string, we force the lexicographical sorting.
This commit fixes this bug and improves the performance, and at the same
time simplifies the implementation. This does not mean I'm smart today,
it means I was stupid when I committed the original implementation ;)
Sentinel: reply -IDONTKNOW to get-master-addr-by-name on lack of info.
If we don't have any clue about a master since it never replied to INFO
so far, reply with an -IDONTKNOW error to SENTINEL
get-master-addr-by-name requests.
Sentinel: more easy master redirection if master is a slave.
Before this commit Sentienl used to redirect master ip/addr if the
current instance reported to be a slave only if this was the first INFO
output received, and the role was found to be slave.
Now instead also if we find that the runid is different, and the
reported role is slave, we also redirect to the reported master ip/addr.
This unifies the behavior of Sentinel in the case of a reboot (where it
will see the first INFO output with the wrong role and will perform the
redirection), with the behavior of Sentinel in the case of a change in
what it sees in the INFO output of the master.
antirez [Fri, 31 Aug 2012 13:32:57 +0000 (15:32 +0200)]
Send an async PING before starting replication with master.
During the first synchronization step of the replication process, a Redis
slave connects with the master in a non blocking way. However once the
connection is established the replication continues sending the REPLCONF
command, and sometimes the AUTH command if needed. Those commands are
send in a partially blocking way (blocking with timeout in the order of
seconds).
Because it is common for a blocked master to accept connections even if
it is actually not able to reply to the slave requests, it was easy for
a slave to block if the master had serious issues, but was still able to
accept connections in the listening socket.
For this reason we now send an asynchronous PING request just after the
non blocking connection ended in a successful way, and wait for the
reply before to continue with the replication process. It is very
unlikely that a master replying to PING can't reply to the other
commands.
This solution was proposed by Didier Spezia (Thanks!) so that we don't
need to turn all the replication process into a non blocking affair, but
still the probability of a slave blocked is minimal even in the event of
a failing master.
Also we now use getsockopt(SO_ERROR) in order to check errors ASAP
in the event handler, instead of waiting for actual I/O to return an
error.
antirez [Fri, 31 Aug 2012 09:08:53 +0000 (11:08 +0200)]
Scripting: Reset Lua fake client reply_bytes after command execution.
Lua scripting uses a fake client in order to run commands in the context
of a client, accumulate the reply, and convert it into a Lua object
to return to the caller. This client is reused again and again, and is
referenced by the server.lua_client globally accessible pointer.
However after every call to redis.call() or redis.pcall(), that is
handled by the luaRedisGenericCommand() function, the reply_bytes field
of the client was not set back to zero. This filed is used to estimate
the amount of memory currently used in the reply. Because of the lack of
reset, script after script executed, this value used to get bigger and
bigger, and in the end on 32 bit systems it triggered the following
assert:
On 64 bit systems this does not happen because it takes too much time to
reach values near to 2^64 for users to see the practical effect of the
bug.
Now in the cleanup stage of luaRedisGenericCommand() we reset the
reply_bytes counter to zero, avoiding the issue. It is not practical to
add a test for this bug, but the fix was manually tested using a
debugger.
antirez [Tue, 28 Aug 2012 15:45:01 +0000 (17:45 +0200)]
Sentinel: Sentinel-side support for slave priority.
The slave priority that is now published by Redis in INFO output is
now used by Sentinel in order to select the slave with minimum priority
for promotion, and in order to consider slaves with priority set to 0 as
not able to play the role of master (they will never be promoted by
Sentinel).
The "slave-priority" field is now one of the fileds that Sentinel
publishes when describing an instance via the SENTINEL commands such as
"SENTINEL slaves mastername".
antirez [Tue, 28 Aug 2012 15:20:26 +0000 (17:20 +0200)]
Sentinel: Redis-side support for slave priority.
A Redis slave can now be configured with a priority, that is an integer
number that is shown in INFO output and can be get and set using the
redis.conf file or the CONFIG GET/SET command.
This field is used by Sentinel during slave election. A slave with lower
priority is preferred. A slave with priority zero is never elected (and
is considered to be impossible to elect even if it is the only slave
available).
A next commit will add support in the Sentinel side as well.
antirez [Fri, 24 Aug 2012 17:28:44 +0000 (19:28 +0200)]
Incrementally flush RDB on disk while loading it from a master.
This fixes issue #539.
Basically if there is enough free memory the OS may buffer the RDB file
that the slave transfers on disk from the master. The file may
actually be flused on disk at once by the operating system when it gets
closed by Redis, causing the close system call to block for a long time.
This patch is a modified version of one provided by yoav-steinberg of
@garantiadata (the original version was posted in the issue #539
comments), and tries to flush the OS buffers incrementally (every 8 MB
of loaded data).
antirez [Fri, 24 Aug 2012 10:55:37 +0000 (12:55 +0200)]
Better Out of Memory handling.
The previous implementation of zmalloc.c was not able to handle out of
memory in an application-specific way. It just logged an error on
standard error, and aborted.
The result was that in the case of an actual out of memory in Redis
where malloc returned NULL (In Linux this actually happens under
specific overcommit policy settings and/or with no or little swap
configured) the error was not properly logged in the Redis log.
This commit fixes this problem, fixing issue #509.
Now the out of memory is properly reported in the Redis log and a stack
trace is generated.
The approach used is to provide a configurable out of memory handler
to zmalloc (otherwise the default one logging the event on the
standard output is used).
antirez [Fri, 24 Aug 2012 10:29:54 +0000 (12:29 +0200)]
Sentinel: send SCRIPT KILL on -BUSY reply and SDOWN instance.
From the point of view of Redis an instance replying -BUSY is down,
since it is effectively not able to reply to user requests. However
a looping script is a recoverable condition in Redis if the script still
did not performed any write to the dataset. In that case performing a
fail over is not optimal, so Sentinel now tries to restore the normal server
condition killing the script with a SCRIPT KILL command.
If the script already performed some write before entering an infinite
(or long enough to timeout) loop, SCRIPT KILL will not work and the
fail over will be triggered anyway.
antirez [Tue, 21 Aug 2012 15:31:44 +0000 (17:31 +0200)]
redis-benchmark: disable big buffer cleanup in hiredis context.
This new hiredis features allows us to reuse a previous context reader
buffer even if already very big in order to maximize performances with
big payloads (Usually hiredis re-creates buffers when they are too big
and unused in order to save memory).
antirez [Fri, 3 Aug 2012 10:39:13 +0000 (12:39 +0200)]
Sentinel: SENTINEL FAILOVER command implemented.
This command can be used in order to force a Sentinel instance to start
a failover for the specified master, as leader, forcing the failover
even if the master is up.
The commit also adds some minor refactoring and other improvements to
functions already implemented that make them able to work when the
master is not in SDOWN condition. For instance slave selection
assumed that we ask INFO every second to every slave, this is true
only when the master is in SDOWN condition, so slave selection did not
worked when the master was not in SDOWN condition.
This commit adds support to optionally execute a script when one of the
following events happen:
* The failover starts (with a slave already promoted).
* The failover ends.
* The failover is aborted.
The script is called with enough parameters (documented in the example
sentinel.conf file) to provide information about the old and new ip:port
pair of the master, the role of the sentinel (leader or observer) and
the name of the master.
The goal of the script is to inform clients of the configuration change
in a way specific to the environment Sentinel is running, that can't be
implemented in a genereal way inside Sentinel itself.
Sentinel: when leader in wait-start, sense another leader as race.
When we are in wait start, if another leader (or any other external
entity) turns a slave into a master, abort the failover, and detect it
as an observer.
Note that the wait-start state is mainly there for this reason but the
abort was yet not implemented.
This adds a new sentinel event -failover-abort-race.
Michael Parker [Thu, 26 Jul 2012 06:51:22 +0000 (23:51 -0700)]
Use correct variable name for value to convert.
Note by @antirez: this code was never compiled because utils.c lacked the
float.h include, so we never noticed this variable was mispelled in the
past.
This should provide a noticeable speed boost when saving certain types
of databases with many sorted sets inside.
Sentinel: abort failover when in wait-start if master is back.
When we are a Leader Sentinel in wait-start state, starting with this
commit the failover is aborted if the master returns online.
This improves the way we handle a notable case of net split, that is the
split between Sentinels and Redis servers, that will be a very common
case of split becase Sentinels will often be installed in the client's
network and servers can be in a differnt arm of the network.
When Sentinels and Redis servers are isolated the master is in ODOWN
condition since the Sentinels can agree about this state, however the
failover does not start since there are no good slaves to promote (in
this specific case all the slaves are unreachable).
However when the split is resolved, Sentinels may sense the slave back
a moment before they sense the master is back, so the failover may start
without a good reason (since the master is actually working too).
Now this condition is reversible, so the failover will be aborted
immediately after if the master is detected to be working again, that
is, not in SDOWN nor in ODOWN condition.
Sentinel: abort failover if no good slave is available.
The previous behavior of the state machine was to wait some time and
retry the slave selection, but this is not robust enough against drastic
changes in the conditions of the monitored instances.
What we do now when the slave selection fails is to abort the failover
and return back monitoring the master. If the ODOWN condition is still
present a new failover will be triggered and so forth.
This commit also refactors the code we use to abort a failover.
When we reset the master we should start with clean timestamps for ping
replies otherwise we'll detect a spurious +sdown event, because on
+master-switch event the previous master instance was probably in +sdown
condition. Since we updated the address we should count time from
scratch again.
Also this commit makes sure to explicitly reset the count of pending
commands, now we can do this because of the new way the hiredis link
is closed.
Sentinel: changes to connection handling and redirection.
We disconnect the Redis instances hiredis link in a more robust way now.
Also we change the way we perform the redirection for the +switch-master
event, that is not just an instance reset with an address change.
Using the same system we now implement the +redirect-to-master event
that is triggered by an instance that is configured to be master but
found to be a slave at the first INFO reply. In that case we monitor the
master instead, logging the incident as an event.
Sentinel: more robust failover detection as observer.
Sentinel observers detect failover checking if a slave attached to the
monitored master turns into its replication state from slave to master.
However while this change may in theory only happen after a SLAVEOF NO
ONE command, in practie it is very easy to reboot a slave instance with
a wrong configuration that turns it into a master, especially if it was
a past master before a successfull failover.
This commit changes the detection policy so that if an instance goes
from slave to master, but at the same time the runid has changed, we
sense a reboot, and in that case we don't detect a failover at all.
This commit also introduces the "reboot" sentinel event, that is logged
at "warning" level (so this will trigger an admin notification).
The commit also fixes a problem in the disconnect handler that assumed
that the instance object always existed, that is not the case. Now we
no longer assume that redisAsyncFree() will call the disconnection
handler before returning.
This commit implements the first, beta quality implementation of Redis
Sentinel, a distributed monitoring system for Redis with notification
and automatic failover capabilities.
Allow Pub/Sub in contexts where other commands are blocked.
Redis loading data from disk, and a Redis slave disconnected from its
master with serve-stale-data disabled, are two conditions where
commands are normally refused by Redis, returning an error.
However there is no reason to disable Pub/Sub commands as well, given
that this layer does not interact with the dataset. To allow Pub/Sub in
as many contexts as possible is especially interesting now that Redis
Sentinel uses Pub/Sub of a Redis master as a communication channel
between Sentinels.
This commit allows Pub/Sub to be used in the above two contexts where
it was previously denied.
For the C standard char can be either signed or unsigned, it's up to the
compiler, but Redis assumed that it was signed in a few places.
The practical effect of this patch is that now Redis 2.6 will run
correctly in every system where char is unsigned, notably the RaspBerry
PI and other ARM systems with GCC.
Thanks to Georgi Marinov (@eesn on twitter) that reported the problem
and allowed me to use his RaspBerry via SSH to trace and fix the issue!
Saj Goonatilleke [Mon, 16 Jul 2012 05:33:25 +0000 (15:33 +1000)]
Truncate short write from the AOF
If Redis only manages to write out a partial buffer, the AOF file won't
load back into Redis the next time it starts up. It is better to
discard the short write than waste time running redis-check-aof.
Saj Goonatilleke [Tue, 17 Jul 2012 02:06:53 +0000 (12:06 +1000)]
New in INFO: aof_last_bgrewrite_status
Behaves like rdb_last_bgsave_status -- even down to reporting 'ok' when
no rewrite has been done yet. (You might want to check that
aof_last_rewrite_time_sec is not -1.)
REDIS_REPL_PING_SLAVE_PERIOD controls how often the master should
transmit a heartbeat (PING) to its slaves. This period, which defaults
to 10, is measured in seconds.
Redis 2.4 masters used to ping their slaves every ten seconds, just like
it says on the tin.
The Redis 2.6 masters I have been experimenting with, on the other hand,
ping their slaves *every second*. (master_last_io_seconds_ago never
approaches 10.) I think the ping period was inadvertently slashed to
one-tenth of its nominal value around the time REDIS_HZ was introduced.
This commit reintroduces correct ping schedule behaviour.
antirez [Tue, 26 Jun 2012 07:47:47 +0000 (09:47 +0200)]
REPLCONF internal command introduced.
The REPLCONF command is an internal command (not designed to be directly
used by normal clients) that allows a slave to set some replication
related state in the master before issuing SYNC to start the
replication.
The initial motivation for this command, and the only reason currently
it is used by the implementation, is to let the slave instance
communicate its listening port to the slave, so that the master can
show all the slaves with their listening ports in the "replication"
section of the INFO output.
This allows clients to auto discover and query all the slaves attached
into a master.
Currently only a single option of the REPLCONF command is supported, and
it is called "listening-port", so the slave now starts the replication
process with something like the following chat:
REPLCONF listening-prot 6380
SYNC
Note that this works even if the master is an older version of Redis and
does not understand REPLCONF, because the slave ignores the REPLCONF
error.
In the future REPLCONF can be used for partial replication and other
replication related features where there is the need to exchange
information between master and slave.
NOTE: This commit also fixes a bug: the INFO outout already carried
information about slaves, but the port was broken, and was obtained
with getpeername(2), so it was actually just the ephemeral port used
by the slave to connect to the master as a client.
antirez [Thu, 21 Jun 2012 09:50:01 +0000 (11:50 +0200)]
Fixed a timing attack on AUTH (Issue #560).
The way we compared the authentication password using strcmp() allowed
an attacker to gain information about the password using a well known
class of attacks called "timing attacks".
The bug appears to be practically not exploitable in most modern systems
running Redis since even using multiple bytes of differences in the
input at a time instead of one the difference in running time in in the
order of 10 nanoseconds, making it hard to exploit even on LAN. However
attacks always get better so we are providing a fix ASAP.
The new implementation uses two fixed length buffers and a constant time
comparison function, with the goal of:
1) Completely avoid leaking information about the content of the
password, since the comparison is always performed between 512
characters and without conditionals.
2) Partially avoid leaking information about the length of the
password.
About "2" we still have a stage in the code where the real password and
the user provided password are copied in the static buffers, we also run
two strlen() operations against the two inputs, so the running time
of the comparison is a fixed amount plus a time proportional to
LENGTH(A)+LENGTH(B). This means that the absolute time of the operation
performed is still related to the length of the password in some way,
but there is no way to change the input in order to get a difference in
the execution time in the comparison that is not just proportional to
the string provided by the user (because the password length is fixed).
Thus in practical terms the user should try to discover LENGTH(PASSWORD)
looking at the whole execution time of the AUTH command and trying to
guess a proportionality between the whole execution time and the
password length: this appears to be mostly unfeasible in the real world.
Also protecting from this attack is not very useful in the case of Redis
as a brute force attack is anyway feasible if the password is too short,
while with a long password makes it not an issue that the attacker knows
the length.
antirez [Fri, 15 Jun 2012 08:03:25 +0000 (10:03 +0200)]
Fix c->reply_bytes computation in setDeferredMultiBulkLength()
In order to implement reply buffer limits introduced in 2.6 and useful
to close the connection under user-selected circumastances of big output
buffers (for instance slow consumers in pub/sub, a blocked slave, and so
forth) Redis takes a counter with the amount of used memory in objects
inside the output list stored into c->reply.
The computation was broken in the function setDeferredMultiBulkLength(),
in the case the object was glued with the next one. This caused the
c->reply_bytes field to go out of sync, be subtracted more than needed,
and wrap back near to ULONG_MAX values.
This commit fixes this bug and adds an assertion that is able to trap
this class of problems.
This problem was discovered looking at the INFO output of an unrelated
issue (issue #547).
antirez [Thu, 14 Jun 2012 13:59:25 +0000 (15:59 +0200)]
ziplistFind(): don't assume that entries are comparable by encoding.
Because Redis 2.6 introduced new integer encodings it is no longer true
that if two entries have a different encoding they are not equal.
An old ziplist can be loaded from an RDB file generated with Redis 2.4,
in this case for instance a small unsigned integers is encoded with a
16 bit encoding, while in Redis 2.6 a more specific 8 bit encoding
format is used.
Because of this bug hashes ended with duplicated values or fields lookup
failed, causing many bad behaviors.
This in turn caused a crash while converting the ziplist encoded hash into
a real hash table because an assertion was raised on duplicated elements.
This commit fixes issue #547.
Many thanks to Pinterest's Marty Weiner and colleagues for discovering
the problem and helping us in the debugging process.
Ted Nyman [Wed, 13 Jun 2012 05:35:00 +0000 (22:35 -0700)]
Standardize punctuation in redis-cli help.
Right there is a mix of help entries ending with periods or
without periods. This standardizes the end of command as without
periods, which seems to be the general custom in most unix tools,
at least.
antirez [Tue, 12 Jun 2012 13:20:16 +0000 (15:20 +0200)]
Added a new hash fuzzy tester.
The new fuzzy tester also removes elements from the hash instead of just
adding random fields. This should increase the probability to find bugs
in the implementations of the hash type internal representations.
antirez [Mon, 11 Jun 2012 21:44:34 +0000 (23:44 +0200)]
Dump ziplist hex value on failed assertion.
The ziplist -> hashtable conversion code is triggered every time an hash
value must be promoted to a full hash table because the number or size of
elements reached the threshold.
If a problem in the ziplist causes the same field to be present
multiple times, the assertion of successful addition of the element
inside the hash table will fail, crashing server with a failed
assertion, but providing little information about the problem.
This code adds a new logging function to perform the hex dump of binary
data, and makes sure that the ziplist -> hashtable conversion code uses
this new logging facility to dump the content of the ziplist when the
assertion fails.
This change was originally made in order to investigate issue #547.
antirez [Sat, 2 Jun 2012 21:29:57 +0000 (23:29 +0200)]
EVAL replication test: less false positives.
wait_for_condition is now used instead of the usual "after 1000" (that
is the way to sleep in Tcl). This should avoid to find the replica in
a state where it is loading the RDB in memory, returning -LOADING error.
This test used to fail when running the test over valgrind, due to the
added latencies.
Alex Mitrofanov [Sat, 2 Jun 2012 01:48:45 +0000 (18:48 -0700)]
Fixed RESTORE hash failure (Issue #532)
(additional commit notes by antirez@gmail.com):
The rdbIsObjectType() macro was not updated when the new RDB object type
of ziplist encoded hashes was added.
As a result RESTORE, that uses rdbLoadObjectType(), failed when a
ziplist encoded hash was loaded.
This does not affected normal RDB loading because in that case we use
the lower-level function rdbLoadType().
antirez [Sat, 2 Jun 2012 08:21:57 +0000 (10:21 +0200)]
RDB type loading functions clarified in comments.
Improved comments to make clear that rdbLoadType() just loads a
general TYPE in the context of RDB that can be an object type or an
expire type, end-of-file, and so forth.
While rdbLoadObjectType() enforces that the type is a valid Object Type
otherwise it returns -1.
antirez [Thu, 31 May 2012 19:45:39 +0000 (21:45 +0200)]
BITOP bug when called against non existing keys fixed.
In the issue #529 an user reported a bug that can be triggered with the
following code:
flushdb
set a
"\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"
bitop or x a b
The bug was introduced with the speed optimization in commit 8bbc076
that specializes every BITOP operation loop up to the minimum length of
the input strings.
However the computation of the minimum length contained an error when a
non existing key was present in the input, after a key that was non zero
length.
This commit fixes the bug and adds a regression test for it.
antirez [Fri, 25 May 2012 10:11:30 +0000 (12:11 +0200)]
Four new persistence fields in INFO. A few renamed.
The 'persistence' section of INFO output now contains additional four
fields related to RDB and AOF persistence:
rdb_last_bgsave_time_sec Duration of latest BGSAVE in sec.
rdb_current_bgsave_time_sec Duration of current BGSAVE in sec.
aof_last_rewrite_time_sec Duration of latest AOF rewrite in sec.
aof_current_rewrite_time_sec Duration of current AOF rewrite in sec.
The 'current' fields are set to -1 if a BGSAVE / AOF rewrite is not in
progress. The 'last' fileds are set to -1 if no previous BGSAVE / AOF
rewrites were performed.
Additionally a few fields in the persistence section were renamed for
consistency:
After the renaming, fields in the persistence section start with rdb_ or
aof_ prefix depending on the persistence method they describe.
The field 'loading' and related fields are not prefixed because they are
unique for both the persistence methods.
antirez [Wed, 23 May 2012 20:12:50 +0000 (22:12 +0200)]
BITOP command 10x speed improvement.
This commit adds a fast-path to the BITOP that can be used for all the
bytes from 0 to the minimal length of the string, and if there are
at max 16 input keys.
Often the intersected bitmaps are roughly the same size, so this
optimization can provide a 10x speed boost to most real world usages
of the command.
Bytes are processed four full words at a time, in loops specialized
for the specific BITOP sub-command, without the need to check for
length issues with the inputs (since we run this algorithm only as far
as there is data from all the keys at the same time).
The remaining part of the string is intersected in the usual way using
the slow but generic algorith.
It is possible to do better than this with inputs that are not roughly
the same size, sorting the input keys by length, by initializing the
result string in a smarter way, and noticing that the final part of the
output string composed of only data from the longest string does not
need any proecessing since AND, OR and XOR against an empty string does
not alter the output (zero in the first case, and the original string in
the other two cases).
More implementations will be implemented later likely, but this should
be enough to release Redis 2.6-RC4 with bitops merged in.
Note: this commit also adds better testing for BITOP NOT command, that
is currently the faster and hard to optimize further since it just
flips the bits of a single input string.
antirez [Tue, 22 May 2012 15:40:20 +0000 (17:40 +0200)]
BITOP: handle integer encoded objects correctly.
A bug in the implementation caused BITOP to crash the server if at least
one one of the source objects was integer encoded.
The new implementation takes an additional array of Redis objects
pointers and calls getDecodedObject() to get a reference to a string
encoded object, and then uses decrRefCount() to release the object.
Tests modified to cover the regression and improve coverage.
antirez [Sun, 20 May 2012 19:34:58 +0000 (21:34 +0200)]
BITCOUNT performance improved.
At Redis's default optimization level the command is now much faster,
always using a constant-time bit manipualtion technique to count bits
instead of GCC builtin popcount, and unrolling the loop.
The current implementation performance is 1.5GB/s in a MBA 11" (1.8 Ghz
i7) compiled with both GCC and clang.
antirez [Sun, 20 May 2012 09:06:29 +0000 (11:06 +0200)]
bitop.c renamed bitops.c
bitop.c contains the "Bit related string operations" so it seems more
logical to call it bitops instead of bitop.
This also makes it matching the name of the test (unit/bitops.tcl).
antirez [Sun, 20 May 2012 09:03:54 +0000 (11:03 +0200)]
Bit operations tests improved.
Fuzzing tests of BITCOUNT / BITOP are iterated multiple times.
The new BITCOUNT fuzzing test uses random strings in a wider interval of
lengths including zero-len strings.
antirez [Sat, 19 May 2012 22:49:35 +0000 (00:49 +0200)]
popcount() optimization for speed.
We run the array by 32 bit words instead of processing it byte per byte.
If the code is compiled using GCC __builtin_popcount() builtin function
is used instead.
antirez [Sat, 19 May 2012 14:16:25 +0000 (16:16 +0200)]
BITCOUNT refactoring.
The low level popualtion counting function is now separated from the
BITCOUNT command implementation, so that the low level function can be
further optimized and eventually used in other contexts if needed.
antirez [Sat, 19 May 2012 08:33:20 +0000 (10:33 +0200)]
Bit-related string operations moved to bitop.c
All the general string operations are implemented in t_string.c, however
the bit operations, while targeting the string type, are better served
in a specific file where we have the implementations of the following
four commands and helper functions:
GETBIT
SETBIT
BITOP
BITCOUNT
In the future this file will probably contain more code related to
making the BITOP and BITCOUNT operations faster.
antirez [Thu, 17 May 2012 13:50:44 +0000 (15:50 +0200)]
BITOP and BITCOUNT tests.
The Redis implementation is tested against Tcl implementations of the
same operation. Both fuzzing and testing of specific aspects of the
commands behavior are performed.
antirez [Wed, 16 May 2012 14:23:09 +0000 (16:23 +0200)]
New commands: BITOP and BITCOUNT.
The motivation for this new commands is to be search in the usage of
Redis for real time statistics. See the article "Fast real time metrics
using Redis".
In general Redis strings when used as bitmaps using the SETBIT/GETBIT
command provide a very space-efficient and fast way to store statistics.
For instance in a web application with users, every user can be
associated with a key that shows every day in which the user visited the
web service. This information can be really valuable to extract user
behaviour information.
With Redis bitmaps doing this is very simple just saying that a given
day is 0 (the data the service was put online) and all the next days are
1, 2, 3, and so forth. So with SETBIT it is possible to set the bit
corresponding to the current day every time the user visits the site.
It is possible to take the count of the bit sets on the run, this is
extremely easy using a Lua script. However a fast bit count native
operation can be useful, especially if it can operate on ranges, or when
the string is small like in the case of days (even if you consider many
years it is still extremely little data).
For this reason BITOP was introduced. The command counts the number of
bits set to 1 in a string, with optional range:
BITCOUNT key [start end]
The start/end parameters are similar to GETRANGE. If omitted the whole
string is tested.
Population counting is more useful when bit-level operations like AND,
OR and XOR are avaialble. For instance I can test multiple users to see
the number of days three users visited the site at the same time. To do
this we can take the AND of all the bitmaps, and then count the set bits.
In the special case of NOT (that inverts the bits) only one source key
can be passed.
The judicious use of BITCOUNT and BITOP combined can lead to interesting
use cases with very space efficient representation of data.
The implementation provided is still not tested and optimized for speed,
next commits will introduce unit tests. Later the implementation will be
profiled to see if it is possible to gain an important amount of speed
without making the code much more complex.
projects / redis.git / log
