Feature Request - Count(start, limit) and Delete(start, limit)

[cmumford]

Original issue 113 created by sawloo on 2012-09-04T22:18:53.000Z:

Count(start, limit)

seems that some people also want a count/size method without calling the iterator to loop thru the entire set just to count the number of records. So, would be great if there is a method like "Count(start, limit)" or "Count(range)" to count the number of records which fall inside the range [start, limit).

Delete(start, limit)

A fast Delete methods which delete a range of keys [start, limit) would be nice. I guess this can be optimized inside levelDB to do this instead of having my program looping and delete one by one.

[cmumford]

Comment #1 originally posted by alexkarpenko on 2012-09-15T23:35:26.000Z:

Similarly, it'd be great if we could get the size of an entry, without also fetching the value from disk.

[cmumford]

Comment #2 originally posted by [email protected] on 2012-09-18T17:18:47.000Z:

There is no way to implement Count more efficiently inside leveldb than outside.

"Delete range" could theoretically be implemented more efficiently inside leveldb, but it would be very complicated or would interact badly with snapshots. So it won't happen any time soon.

[cmumford]

Comment #3 originally posted by earonesty on 2014-07-10T18:44:29.000Z:

If a fast count is important, you can keep track of the count as you write entries, and write it out as it's own special entry.

# pseudo 
if (!get(k)) {
   put(k,v)
   c=get("*cnt");
   ++c;
   put("*cnt",v)
} else {
   put(k,v)
}