https://bugs.openldap.org/show_bug.cgi?id=10402

Issue ID: 10402 Summary: Feature request: parameter for mdb_env_copy to exclude databases Product: LMDB Version: unspecified Hardware: All OS: All Status: UNCONFIRMED Keywords: needs_review Severity: normal Priority: --- Component: liblmdb Assignee: bugs@openldap.org Reporter: jeffro256@tutanota.com Target Milestone: ---

## Desired behavior

New overload or API modification to `mdb_env_copy{...}()` which allows passing a list of names of databases to exclude from the environment copy.

## Example use-case

The Monero blockchain database [1] has the option to derived a "pruned" database for space-saving purposes. This removes some ~60% of data which some users may find non-essential. Currently, the pruning code [2] copies each non-pruned table manually, specifying key ordering functions, DB flags, etc. It then drops some entries from the relevant "prunable tables". This, however, adds technical maintenance debt when databases are added/updated. A preferable alternative would be to write high-level modification code once and use an overload of `mdb_env_copy` which excludes copying database that we know in advance we don't want to copy. Then our pruning utility would work agnostic to database changes.

## Why

Adding this functionality ourselves would involve re-writing large portions of `mdb_env_copyfd{0,1}` and `mdb_env_cwalk`, which requires either A) vendoring LMDB, or B) possibly breaking in future updates.

You may understandably be of the opinion that the maintenance burden is an "us problem", and not deem pursuing this feature request worth it, but hopefully you seem the value in this utility. Thanks for y'alls hard work on LMDB.

## Links

[1] https://github.com/monero-project/monero/blob/d32b5bfe18e2f5b979fa8dc3a8966c... [2] https://github.com/monero-project/monero/blob/master/src/blockchain_utilitie...