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[redis.git] / TODO

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-Redis TODO and Roadmap
+Redis TODO
+----------

 
 

-VERSION 1.4 TODO (Hash type)
-============================
+WARNING: are you a possible Redis contributor?
+         Before implementing what is listed what is listed in this file
+         please drop a message in the Redis google group or chat with
+         antirez or pietern on irc.freenode.org #redis to check if the work
+         is already in progress and if the feature is still interesting for
+         us, and *how* exactly this can be implemented to have good changes
+         of a merge. Otherwise it is probably wasted work! Thank you

 
 

-* BRPOPLPUSH
-* List ops like L/RPUSH L/RPOP should return the new list length.
-* Save dataset / fsync() on SIGTERM
-* MULTI/EXEC should support the "EXEC FSYNC" form?
-* BLPOP & C. tests (write a non blocking Tcl client as first step)
+DISKSTORE TODO
+==============

 
 

-Virtual Memory sub-TODO:
-* Check if the page selection algorithm is working well
-* Divide swappability of objects by refcount
-* it should be possible to give the vm-max-memory option in megabyte, gigabyte, ..., just using 2GB, 100MB, and so forth.
-* Try to understand what can be moved into I/O threads that currently is instead handled by the main thread. For instance swapping file table scannig to find contiguous page could be a potential candidate (but I'm not convinced it's a good idea, better to improve the algorithm, for instance double the fast forward at every step?).
-* Possibly decrRefCount() against swapped objects can be moved into I/O threads, as it's a slow operation against million elements list, and in general consumes CPU time that can be consumed by other threads (and cores).
-* EXISTS should avoid loading the object if possible without too make the code too specialized.
-* vm-min-age <seconds> option
-* Make sure objects loaded from the VM are specially encoded when possible.
-* Check what happens performance-wise if instead to create threads again and again the same threads are reused forever. Note: this requires a way to disable this clients in the child, but waiting for empty new jobs queue can be enough.
+* Fix FLUSHALL/FLUSHDB: the queue of pending reads/writes should be handled.
+* Check that 00/00 and ff/ff exist at startup, otherwise exit with error.
+* Implement sync flush option, where data is written synchronously on disk when a command is executed.
+* Implement MULTI/EXEC as transaction abstract API to diskstore.c, with transaction_start, transaction_end, and a journal to recover.
+* Stop BGSAVE thread on shutdown and any other condition where the child is killed during normal bgsave.
+* Fix RANDOMKEY to really do something interesting
+* Fix DBSIZE to really do something interesting
+* Add a DEBUG command to check if an entry is or not in memory currently

 
 

-* Hashes (GET/SET/DEL/INCRBY/EXISTS/FIELDS/LEN/MSET/MGET). Special encoding for hashes with < N keys.
+* dscache.c near 236, kobj = createStringObject... we could use static obj.

 
 

-VERSION 2.2 TODO (Fault tolerant sharding)
-===========================================
+APPEND ONLY FILE
+================

 
 

-* Redis-cluster, a fast intermediate layer (proxy) that implements consistent hashing and fault tollerant nodes handling.
+* in AOF rewirte use HMSET to rewrite small hashes instead of multiple calls
+  to HSET.

 
 

-Interesting readings about this:
+OPTIMIZATIONS
+=============

 
 

-    - http://ayende.com/Blog/archive/2009/04/06/designing-rhino-dht-a-fault-tolerant-dynamically-distributed-hash.aspx
-
-VERSION 2.4 TODO (Optimizations and latency)
-============================================
-
-* Lower the CPU usage.
-* Lower the RAM usage everywhere possible.
-* Use epool and alike to rewrite ae.c for Linux and other platforms suppporting fater-than-select() mutiplexing APIs.
-* Implement an UDP interface for low-latency GET/SET operations.
-
-OTHER IMPORTANT THINGS THAT WILL BE ADDED BUT I'M NOT SURE WHEN
-===============================================================
+* Avoid COW due to incrementing the dict iterators counter.
+* SORT: Don't copy the list into a vector when BY argument is constant.
+* Write the hash table size of every db in the dump, so that Redis can resize the hash table just one time when loading a big DB.
+* Read-only mode for slaves.
+* Redis big lists as linked lists of small ziplists?
+  Possibly a simple heuristic that join near nodes when some node gets smaller than the low_level, and split it into two if gets bigger than high_level.

 
 

-BIG ONES:
+REPORTING
+=========

 
 

-* Specially encoded memory-saving integer sets.
-* A command to export a JSON dump (there should be mostly working patch needing major reworking).
-* Specially encoded sets of integers (this includes a big refactoring providing an higher level layer for Sets manipulation)
-* ZRANK: http://docs.google.com/viewer?a=v&q=cache:tCQaP3ZeN4YJ:courses.csail.mit.edu/6.046/spring04/handouts/ps5-sol.pdf+skip+list+rank+operation+augmented&hl=en&pid=bl&srcid=ADGEEShXuNjTcZyXw_1cq9OaWpSXy3PprjXqVzmM-LE0ETFznLyrDXJKQ_mBPNT10R8ErkoiXD9JbMw_FaoHmOA4yoGVrA7tZWiy393JwfCwuewuP93sjbkzZ_gnEp83jYhPYjThaIzw&sig=AHIEtbRF0GkYCdYRFtTJBE69senXZwFY0w
+* Better INFO output with sections.

 
 

-SMALL ONES:
+RANDOM
+======

 
 

-* Give errors when incrementing a key that does not look like an integer, when providing as a sorted set score something can't be parsed as a double, and so forth.
-* MSADD (n keys) (n values). See this thread in the Redis google group: http://groups.google.com/group/redis-db/browse_thread/thread/e766d84eb375cd41
-* Don't save empty lists / sets / zsets on disk with snapshotting.
-* Remove keys when a list / set / zset reaches length of 0.
+* Clients should be closed as far as the output buffer list is bigger than a given number of elements (configurable in redis.conf)
+* Should the redis default configuration, and the default redis.conf, just bind 127.0.0.1?

 
 

-THE "MAYBE" TODO LIST: things that may or may not get implemented
-=================================================================
+KNOWN BUGS
+==========

 
 

-Most of this can be seen just as proposals, the fact they are in this list
-it's not a guarantee they'll ever get implemented ;)
+* What happens in the following scenario:
+    1) We are reading an AOF file.
+    2) SETEX FOO 5 BAR
+    3) APPEND FOO ZAP
+    What happens if between 1 and 2 for some reason (system under huge load
+    or alike) too many time passes? We should prevent expires while the
+    AOF is loading.

 
 

-* Move dict.c from hash table to skip list, in order to avoid the blocking resize operation needed for the hash table.
-* FORK command (fork()s executing the commands received by the current
-  client in the new process). Hint: large SORTs can use more cores,
-  copy-on-write will avoid memory problems.
-* DUP command? DUP srckey dstkey, creates an exact clone of srckey value in dstkey.
-* SORT: Don't copy the list into a vector when BY argument is constant.
-* Write the hash table size of every db in the dump, so that Redis can resize the hash table just one time when loading a big DB.
-* LOCK / TRYLOCK / UNLOCK as described many times in the google group
-* Replication automated tests
-* Byte Array type (BA prefixed commands): BASETBIT BAGETBIT BASETU8 U16 U32 U64 S8 S16 S32 S64, ability to atomically INCRBY all the base types. BARANGE to get a range of bytes as a bulk value, BASETRANGE to set a range of bytes.
-* zmalloc() should avoid to add a private header for archs where there is some other kind of libc-specific way to get the size of a malloced block. Already done for Mac OS X.
-* Read-only mode.
-* Pattern-matching replication.
-* Add an option to relax the delete-expiring-keys-on-write semantic *denying* replication and AOF when this is on? Can be handy sometimes, when using Redis for non persistent state, but can create problems. For instance should rename and move also "move" the timeouts? How does this affect other commands?
-* Multiple BY in SORT.