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: [email protected]
Reporter: [email protected]
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/d32b5bfe18e2f5b979fa8dc3a8966c76159ca722/src/blockchain_db/lmdb/db_lmdb.cpp
[2]
https://github.com/monero-project/monero/blob/master/src/blockchain_utilities/blockchain_prune.cpp
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