[redis.git] / TODO

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

VERSION 2.2 TODO (Optimizations and latency)
============================================

* Lower the CPU usage.
* Lower the RAM usage everywhere possible.
* Specially encoded Sets (like Hashes).
* Implement an UDP interface for low-latency operations.
* What about a special coding that is about storing the "rdb" serialized format instead of the actual value? This can be used when we have LRU in order to super-compress data into memory, for data not accessed frequetly. It's a VM-alike strategy but fully in memory, may reduce the space to hold some dataset in an impressive way. Trivial to implement.
* Another idea: LRU does not need to be super precise right? Maybe it's a good idea to just put into the skiplist implementing the LRU just the pointer to the key without evne incr/decr business, nor the need to remove the pointer when the key is deleted. There is to think more about that.

VERSION 2.x TODO
================

* BRPOPLPUSH
* Save dataset / fsync() on SIGTERM
* Change the implementation of ZCOUNT to use the augmented skiplist in order to be much faster.

Virtual Memory optimizations:
* Use multiple open FDs against the VM file, one for thread.
* Check what happens performance-wise if instead of creating 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.
* Implement LEN, PEEK, POKE, SETBIT, GETBIT

OTHER IMPORTANT THINGS THAT WILL BE ADDED BUT I'M NOT SURE WHEN
===============================================================

BIG ONES:

* 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)

SMALL ONES:

* If sizeof(double) == sizeof(void*) we could store the double value of sorted sets directly in place of the pointer instead of allocating it in the heap.
* Delete on writes against expire policy should only happen after argument parsing for commands doing their own arg parsing stuff.
* 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.
* An option to exec a command slave-side if the master connection is lost: even cooler: if the script returns "0" the slave elects itself as master, otherwise continue trying to reconnect.
* PING the master from time to time to check if it's gone.

THE "MAYBE" TODO LIST: things that may or may not get implemented
=================================================================

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 ;)

* 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.

KNOWN BUGS
==========

* LRANGE and other commands are using 32 bit integers for ranges, and overflows are not detected. So LRANGE mylist 0 23498204823094823904823904 will have random effects.
Commit	Line	Data
f284d963	1	Redis TODO and Roadmap
469c4e45	2	----------------------
f284d963	3
469c4e45	4	VERSION 2.2 TODO (Optimizations and latency)
	5	============================================
	6
	7	* Lower the CPU usage.
	8	* Lower the RAM usage everywhere possible.
	9	* Specially encoded Sets (like Hashes).
	10	* Implement an UDP interface for low-latency operations.
	11	* What about a special coding that is about storing the "rdb" serialized format instead of the actual value? This can be used when we have LRU in order to super-compress data into memory, for data not accessed frequetly. It's a VM-alike strategy but fully in memory, may reduce the space to hold some dataset in an impressive way. Trivial to implement.
d6d3f92f	12	* Another idea: LRU does not need to be super precise right? Maybe it's a good idea to just put into the skiplist implementing the LRU just the pointer to the key without evne incr/decr business, nor the need to remove the pointer when the key is deleted. There is to think more about that.
469c4e45	13
469c4e45	14	VERSION 2.x TODO
6766f45e	15	================
23cff1a8	16
b177fd30	17	* BRPOPLPUSH
b177fd30	18	* Save dataset / fsync() on SIGTERM
32a66513	19	* Change the implementation of ZCOUNT to use the augmented skiplist in order to be much faster.
f6b141c5	20
469c4e45	21	Virtual Memory optimizations:
7c775e09	22	* Use multiple open FDs against the VM file, one for thread.
469c4e45	23	* Check what happens performance-wise if instead of creating 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.
a97b9060	24	* Implement LEN, PEEK, POKE, SETBIT, GETBIT
7d65b33d	25
3f477979	26	OTHER IMPORTANT THINGS THAT WILL BE ADDED BUT I'M NOT SURE WHEN
	27	===============================================================
	28
	29	BIG ONES:
	30
	31	* Specially encoded memory-saving integer sets.
	32	* A command to export a JSON dump (there should be mostly working patch needing major reworking).
f0c138f6	33	* Specially encoded sets of integers (this includes a big refactoring providing an higher level layer for Sets manipulation)
3f477979	34
	35	SMALL ONES:
	36
ada386b2	37	* If sizeof(double) == sizeof(void*) we could store the double value of sorted sets directly in place of the pointer instead of allocating it in the heap.
978c2c94	38	* Delete on writes against expire policy should only happen after argument parsing for commands doing their own arg parsing stuff.
3f477979	39	* 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.
25e52257	40	* MSADD (n keys) (n values). See this thread in the Redis google group: http://groups.google.com/group/redis-db/browse_thread/thread/e766d84eb375cd41
f0c138f6	41	* Don't save empty lists / sets / zsets on disk with snapshotting.
f0c138f6	42	* Remove keys when a list / set / zset reaches length of 0.
5921aa36	43	* An option to exec a command slave-side if the master connection is lost: even cooler: if the script returns "0" the slave elects itself as master, otherwise continue trying to reconnect.
3ea27d37	44	* PING the master from time to time to check if it's gone.
3f477979	45
f0c138f6	46	THE "MAYBE" TODO LIST: things that may or may not get implemented
f0c138f6	47	=================================================================
f6b141c5	48
0188805d	49	Most of this can be seen just as proposals, the fact they are in this list
	50	it's not a guarantee they'll ever get implemented ;)
	51
57033301	52	* Move dict.c from hash table to skip list, in order to avoid the blocking resize operation needed for the hash table.
682ac724	53	* FORK command (fork()s executing the commands received by the current
	54	client in the new process). Hint: large SORTs can use more cores,
	55	copy-on-write will avoid memory problems.
	56	* DUP command? DUP srckey dstkey, creates an exact clone of srckey value in dstkey.
	57	* SORT: Don't copy the list into a vector when BY argument is constant.
	58	* 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.
	59	* LOCK / TRYLOCK / UNLOCK as described many times in the google group
	60	* Replication automated tests
	61	* 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.
	62	* 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.
	63	* Read-only mode.
	64	* Pattern-matching replication.
ac945e2d	65	* 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?
f0c138f6	66	* Multiple BY in SORT.
cef34df0	67
	68	KNOWN BUGS
	69	==========
	70
	71	* LRANGE and other commands are using 32 bit integers for ranges, and overflows are not detected. So LRANGE mylist 0 23498204823094823904823904 will have random effects.