Blocking command should not be used with MULTI, LUA, and RM_Call. This is because,
the caller, who executes the command in this context, expects a reply.
Today, LUA and MULTI have a special (and different) treatment to blocking commands:
LUA - Most commands are marked with no-script flag which are checked when executing
and command from LUA, commands that are not marked (like XREAD) verify that their
blocking mode is not used inside LUA (by checking the CLIENT_LUA client flag).
MULTI - Command that is going to block, first verify that the client is not inside
multi (by checking the CLIENT_MULTI client flag). If the client is inside multi, they
return a result which is a match to the empty key with no timeout (for example blpop
inside MULTI will act as lpop)
For modules that perform RM_Call with blocking command, the returned results type is
REDISMODULE_REPLY_UNKNOWN and the caller can not really know what happened.
Disadvantages of the current state are:
No unified approach, LUA, MULTI, and RM_Call, each has a different treatment
Module can not safely execute blocking command (and get reply or error).
Though It is true that modules are not like LUA or MULTI and should be smarter not
to execute blocking commands on RM_Call, sometimes you want to execute a command base
on client input (for example if you create a module that provides a new scripting
language like javascript or python).
While modules (on modules command) can check for REDISMODULE_CTX_FLAGS_LUA or
REDISMODULE_CTX_FLAGS_MULTI to know not to block the client, there is no way to
check if the command came from another module using RM_Call. So there is no way
for a module to know not to block another module RM_Call execution.
This commit adds a way to unify the treatment for blocking clients by introducing
a new CLIENT_DENY_BLOCKING client flag. On LUA, MULTI, and RM_Call the new flag
turned on to signify that the client should not be blocked. A blocking command
verifies that the flag is turned off before blocking. If a blocking command sees
that the CLIENT_DENY_BLOCKING flag is on, it's not blocking and return results
which are matches to empty key with no timeout (as MULTI does today).
The new flag is checked on the following commands:
List blocking commands: BLPOP, BRPOP, BRPOPLPUSH, BLMOVE,
Zset blocking commands: BZPOPMIN, BZPOPMAX
Stream blocking commands: XREAD, XREADGROUP
SUBSCRIBE, PSUBSCRIBE, MONITOR
In addition, the new flag is turned on inside the AOF client, we do not want to
block the AOF client to prevent deadlocks and commands ordering issues (and there
is also an existing assert in the code that verifies it).
To keep backward compatibility on LUA, all the no-script flags on existing commands
were kept untouched. In addition, a LUA special treatment on XREAD and XREADGROUP was kept.
To keep backward compatibility on MULTI (which today allows SUBSCRIBE, and PSUBSCRIBE).
We added a special treatment on those commands to allow executing them on MULTI.
The only backward compatibility issue that this PR introduces is that now MONITOR
is not allowed inside MULTI.
Tests were added to verify blocking commands are not blocking the client on LUA, MULTI,
or RM_Call. Tests were added to verify the module can check for CLIENT_DENY_BLOCKING flag.
Co-authored-by: Oran Agra <oran@redislabs.com>
Co-authored-by: Itamar Haber <itamar@redislabs.com>
Add two optional callbacks to the RedisModuleTypeMethods structure, which is `free_effort`
and `unlink`. the `free_effort` callback indicates the effort required to free a module memory.
Currently, if the effort exceeds LAZYFREE_THRESHOLD, the module memory may be released
asynchronously. the `unlink` callback indicates the key has been removed from the DB by redis, and
may soon be freed by a background thread.
Add `lazyfreed_objects` info field, which represents the number of objects that have been
lazyfreed since redis was started.
Add `RM_GetTypeMethodVersion` API, which return the current redis-server runtime value of
`REDISMODULE_TYPE_METHOD_VERSION`. You can use that when calling `RM_CreateDataType` to know
which fields of RedisModuleTypeMethods are gonna be supported and which will be ignored.
* Introduce a new API's: RM_GetContextFlagsAll, and
RM_GetKeyspaceNotificationFlagsAll that will return the
full flags mask of each feature. The module writer can
check base on this value if the Flags he needs are
supported or not.
* For each flag, introduce a new value on redismodule.h,
this value represents the LAST value and should be there
as a reminder to update it when a new value is added,
also it will be used in the code to calculate the full
flags mask (assuming flags are incrementally increasing).
In addition, stated that the module writer should not use
the LAST flag directly and he should use the GetFlagAll API's.
* Introduce a new API: RM_IsSubEventSupported, that returns for a given
event and subevent, whether or not the subevent supported.
* Introduce a new macro RMAPI_FUNC_SUPPORTED(func) that returns whether
or not a function API is supported by comparing it to NULL.
* Introduce a new API: int RM_GetServerVersion();, that will return the
current Redis version in the format 0x00MMmmpp; e.g. 0x00060008;
* Changed unstable version from 999.999.999 to 255.255.255
Co-authored-by: Oran Agra <oran@redislabs.com>
Co-authored-by: Yossi Gottlieb <yossigo@gmail.com>
The main motivation here is to provide a way for modules to create a
single, global context that can be used for logging.
Currently, it is possible to obtain a thread-safe context that is not
attached to any blocked client by using `RM_GetThreadSafeContext`.
However, the attached context is not linked to the module identity so
log messages produced are not tagged with the module name.
Ideally we'd fix this in `RM_GetThreadSafeContext` itself but as it
doesn't accept the current context as an argument there's no way to do
that in a backwards compatible manner.
This is essentially the same as calling COMMAND GETKEYS but provides a
more efficient interface that can be used in every context (i.e. not a
Redis command).
Added RedisModule_HoldString that either returns a
shallow copy of the given String (by increasing
the String ref count) or a new deep copy of String
in case its not possible to get a shallow copy.
Co-authored-by: Itamar Haber <itamar@redislabs.com>
Diskless master has some inherent latencies.
1) fork starts with delay from cron rather than immediately
2) replica is put online only after an ACK. but the ACK
was sent only once a second.
3) but even if it would arrive immediately, it will not
register in case cron didn't yet detect that the fork is done.
Besides that, when a replica disconnects, it doesn't immediately
attempts to re-connect, it waits for replication cron (one per second).
in case it was already online, it may be important to try to re-connect
as soon as possible, so that the backlog at the master doesn't vanish.
In case it disconnected during rdb transfer, one can argue that it's
not very important to re-connect immediately, but this is needed for the
"diskless loading short read" test to be able to run 100 iterations in 5
seconds, rather than 3 (waiting for replication cron re-connection)
changes in this commit:
1) sync command starts a fork immediately if no sync_delay is configured
2) replica sends REPLCONF ACK when done reading the rdb (rather than on 1s cron)
3) when a replica unexpectedly disconnets, it immediately tries to
re-connect rather than waiting 1s
4) when when a child exits, if there is another replica waiting, we spawn a new
one right away, instead of waiting for 1s replicationCron.
5) added a call to connectWithMaster from replicationSetMaster. which is called
from the REPLICAOF command but also in 3 places in cluster.c, in all of
these the connection attempt will now be immediate instead of delayed by 1
second.
side note:
we can add a call to rdbPipeReadHandler in replconfCommand when getting
a REPLCONF ACK from the replica to solve a race where the replica got
the entire rdb and EOF marker before we detected that the pipe was
closed.
in the test i did see this race happens in one about of some 300 runs,
but i concluded that this race is unlikely in real life (where the
replica is on another host and we're more likely to first detect the
pipe was closed.
the test runs 100 iterations in 3 seconds, so in some cases it'll take 4
seconds instead (waiting for another REPLCONF ACK).
Removing unneeded startBgsaveForReplication from updateSlavesWaitingForBgsave
Now that CheckChildrenDone is calling the new replicationStartPendingFork
(extracted from serverCron) there's actually no need to call
startBgsaveForReplication from updateSlavesWaitingForBgsave anymore,
since as soon as updateSlavesWaitingForBgsave returns, CheckChildrenDone is
calling replicationStartPendingFork that handles that anyway.
The code in updateSlavesWaitingForBgsave had a bug in which it ignored
repl-diskless-sync-delay, but removing that code shows that this bug was
hiding another bug, which is that the max_idle should have used >= and
not >, this one second delay has a big impact on my new test.
- the test now waits for specific set of log messages rather than wait for
timeout looking for just one message.
- we don't wanna sample the current length of the log after an action, due
to a race, we need to start the search from the line number of the last
message we where waiting for.
- when attempting to trigger a full sync, use multi-exec to avoid a race
where the replica manages to re-connect before we completed the set of
actions that should force a full sync.
- fix verify_log_message which was broken and unused
tests were sensitive to additional log lines appearing in the log
causing the search to come empty handed.
instead of just looking for the n last log lines, capture the log lines
before performing the action, and then search from that offset.
The scan key module API provides the scan callback with the current
field name and value (if it exists). Those arguments are RedisModuleString*
which means it supposes to point to robj which is encoded as a string.
Using createStringObjectFromLongLong function might return robj that
points to an integer and so break a module that tries for example to
use RedisModule_StringPtrLen on the given field/value.
The PR introduces a fix that uses the createObject function and sdsfromlonglong function.
Using those function promise that the field and value pass to the to the
scan callback will be Strings.
The PR also changes the Scan test module to use RedisModule_StringPtrLen
to catch the issue. without this, the issue is hidden because
RedisModule_ReplyWithString knows to handle integer encoding of the
given robj (RedisModuleString).
The PR also introduces a new test to verify the issue is solved.
There is an inherent race between the deferring client and the
"main" client of the test: While the deferring client issues a blocking
command, we can't know for sure that by the time the "main" client
tries to issue another command (Usually one that unblocks the deferring
client) the deferring client is even blocked...
For lack of a better choice this commit uses TCL's 'after' in order
to give some time for the deferring client to issues its blocking
command before the "main" client does its thing.
This problem probably exists in many other tests but this commit
tries to fix blockonkeys.tcl
By using a "circular BRPOPLPUSH"-like scenario it was
possible the get the same client on db->blocking_keys
twice (See comment in moduleTryServeClientBlockedOnKey)
The fix was actually already implememnted in
moduleTryServeClientBlockedOnKey but it had a bug:
the funxction should return 0 or 1 (not OK or ERR)
Other changes:
1. Added two commands to blockonkeys.c test module (To
reproduce the case described above)
2. Simplify blockonkeys.c in order to make testing easier
3. cast raxSize() to avoid warning with format spec
Makse sure call() doesn't wrap replicated commands with
a redundant MULTI/EXEC
Other, unrelated changes:
1. Formatting compiler warning in INFO CLIENTS
2. Use CLIENT_ID_AOF instead of UINT64_MAX
If a blocked module client times-out (or disconnects, unblocked
by CLIENT command, etc.) we need to call moduleUnblockClient
in order to free memory allocated by the module sub-system
and blocked-client private data
Other changes:
Made blockedonkeys.tcl tests a bit more aggressive in order
to smoke-out potential memory leaks
With the previous API, a NULL return value was ambiguous and could
represent either an old value of NULL or an error condition. The new API
returns a status code and allows the old value to be returned
by-reference.
This commit also includes test coverage based on
tests/modules/datatype.c which did not exist at the time of the original
commit.
there were two lssues, one is taht BGREWRITEAOF failed since the initial one was still in progress
the solution for this one is to enable appendonly from the server startup so there's no initial aofrw.
the other problem was 0 loading progress events, theory is that on some
platforms a sleep of 1 will cause a much greater delay due to the context
switch, but on other platform it doesn't. in theory a sleep of 100 micro
for 1k keys whould take 100ms, and with hz of 500 we should be gettering
50 events (one every 2ms). in practise it doesn't work like that, so trying
to find a sleep that would be long enough but still not cause the test to take
too long.
- Adding RM_ScanKey
- Adding tests for RM_ScanKey
- Refactoring RM_Scan API
Changes in RM_Scan
- cleanup in docs and coding convention
- Moving out of experimantal Api
- Adding ctx to scan callback
- Dont use cursor of -1 as an indication of done (can be a valid cursor)
- Set errno when returning 0 for various reasons
- Rename Cursor to ScanCursor
- Test filters key that are not strings, and opens a key if NULL
The implementation expose the following new functions:
1. RedisModule_CursorCreate - allow to create a new cursor object for
keys scanning
2. RedisModule_CursorRestart - restart an existing cursor to restart the
scan
3. RedisModule_CursorDestroy - destroy an existing cursor
4. RedisModule_Scan - scan keys
The RedisModule_Scan function gets a cursor object, a callback and void*
(used as user private data).
The callback will be called for each key in the database proving the key
name and the value as RedisModuleKey.
- the API name was odd, separated to two apis one for LRU and one for LFU
- the LRU idle time was in 1 second resolution, which might be ok for RDB
and RESTORE, but i think modules may need higher resolution
- adding tests for LFU and for handling maxmemory policy mismatch
Add two new functions that leverage the RedisModuleDataType mechanism
for RDB serialization/deserialization and make it possible to use it
to/from arbitrary strings:
* RM_SaveDataTypeToString()
* RM_LoadDataTypeFromString()
rename RM_ServerInfoGetFieldNumerical RM_ServerInfoGetFieldSigned
move string2ull to util.c
fix leak in RM_GetServerInfo when duplicate info fields exist
- Add RM_GetServerInfo and friends
- Add auto memory for new opaque struct
- Add tests for new APIs
other minor fixes:
- add const in various char pointers
- requested_section in modulesCollectInfo was actually not sds but char*
- extract new string2d out of getDoubleFromObject for code reuse
Add module API for
* replication hooks: role change, master link status, replica online/offline
* persistence hooks: saving, loading, loading progress
* misc hooks: cron loop, shutdown, module loaded/unloaded
* change the way hooks test work, and add tests for all of the above
startLoading() now gets flag indicating what is loaded.
stopLoading() now gets an indication of success or failure.
adding startSaving() and stopSaving() with similar args and role.
Adding a test for coverage for RM_Call in a new "misc" unit
to be used for various short simple tests
also solves compilation warnings in redismodule.h and fork.c
