[kvdb-rocksdb] adds num_keys()
#285
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Uses `"rocksdb.estimate-num-keys"` to get an estimate of the number of keys in a database (see https://github.com/facebook/rocksdb/wiki/RocksDB-FAQ#failure-recovery).
That's what I did in the other PR but I think I'd like to see a use case outside rocksdb first. Databases vary a lot when it comes to precision and performance of counting the records so not sure it's something we should abstract over. E.g. the memory db impl would likely not be an estimate, and who knows how lmdb works in this area? |
* master: Update benchmark code to latest changes on master (#284)
Co-Authored-By: Andronik Ordian <write@reusable.software>
| Some(ref cfs) => { | ||
| let cf = cfs.cf(col as usize); | ||
| match cfs.db.property_int_value_cf(cf, ESTIMATE_NUM_KEYS) { | ||
| Ok(estimate) => Ok(estimate.unwrap_or_default()), |
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hmm, I'm not sure that I follow the propagation of errors here.
If no db exist => Ok(0)
Ok(None) => only happens on bad &str?!
Err(e) => parsing of number failed or something else?
according to https://github.com/facebook/rocksdb/blob/08809f5e6cd9cc4bc3958dd4d59457ae78c76660/include/rocksdb/db.h#L654-L689 "rocksdb.estimate-num-keys" will succeed so I see no problem with but some errors/Option::None might get swallowed
Uses
"rocksdb.estimate-num-keys"to get an estimate of the number of keys in a database (see https://github.com/facebook/rocksdb/wiki/RocksDB-FAQ#failure-recovery).