Is there anything like memcached, but for sorted lists?

Question

I have a situation where I could really benefit from having system like memcached, but with the ability to store (per each key) sorted list of elements, and modifying the list by addition of values.

For example:

something.add_to_sorted_list( 'topics_list_sorted_by_title', 1234, 'some_title')
something.add_to_sorted_list( 'topics_list_sorted_by_title', 5436, 'zzz')
something.add_to_sorted_list( 'topics_list_sorted_by_title', 5623, 'aaa')

Which I then could use like this:

something.get_list_size( 'topics_list_sorted_by_title' )
// returns 3
something.get_list_elements( 'topics_list_sorted_by_title', 1, 10 )
// returns: 5623, 1234, 5436

Required system would allow me to easily get items count in every array, and fetch any number of values from the array, with the assumption that the values are sorted using attached value.

I hope that the description is clear. And the question is relatively simple: is there any such system?

Answer 1

Take a look at MongoDB. It uses memory mapped files, so is incredibly fast and should perform at a comparative level to MemCached.

MongoDB is a schema-less database that should support what you're looking for (indexing/sorting)

Answer 2

MongoDB will fit. What's important it has indexes, so you can add an index by title for topics collection and then retrieve items sorted by the index:

db.topics.ensureIndex({"title": 1})
db.topics.find().sort({"title": 1})

Answer 3

why not just store an array in memcached? at least in python and PHP the memcached APIs support this (i think python uses pickle but i dont recall for sure).

if you need permanent data storage or backup, memcacheDB uses the same API.

basic pseudopython example:

getting stored data stored=cache.get(storedDataName)

initialize list if you have not stored anything previously if(stored==None): stored={}

---------------- finding stored items

try: alreadyHaveItem=stored[itemKey] except KeyError: print 'no result in cached'

---------------- adding new items

for item in newItemsDict: stored[item]=newItems[item]

---------------- saving the results in cache cache.set(storedDataName,stored,TTL)

Answer 4

Redis supports lists and sets. You can diasable disk saving and use it like memcache instead of going for MongoDB which would save things to disk.