Question

I am working on a Distributed key-value system (or data-store), which uses levelDB as its embedded database library in the back-end.

I want one node/machine to host multiple tables (for the purpose of replication and load-balancing). I understand levelDB has no notion of tables, so I cannot logically partition my data in form of tables (hence cannot use these tables as my basic unit of distribution).

My question is: is there a provision of having multiple ‘logical tables’ in single instance of levelDB ?

From what I know, I can have multiple instances of levelDB running on my node each handling one table. But I do not want to do that, since in this case there will be serious contention (at disk I believe) when these multiple DB instances are accessed simultaneously. While having multiple logical tables in single instance of DB can give me advantages of levelDB optimizations for minimizing disk accesses.

Answer 1

If you want to have multiple “logical tables” in LevelDB, then you have to partition your key space or add a prefix to the keys. For each table create a different prefix, eg:

0x0001 is for table 1
0x0002 is for table 2
0x0003 is for table 3
and so on...

So a key would consist of the table prefix and the key itself: [0x0001,0xFF11] would address key 0xFF11 in table 1. You can then use a single LevelDB instance and have multiple “key spaces” which would correspond to “tables”.