ylavic commented on code in PR #49:
URL: https://github.com/apache/apr/pull/49#discussion_r1370436413
##########
dbm/apr_dbm_lmdb.c:
##########
@@ -156,14 +168,16 @@ static void vt_lmdb_close(apr_dbm_t *dbm)
{
real_file_t *f = dbm->file;
- if (f->cursor) {
- mdb_cursor_close(f->cursor);
- f->cursor = NULL;
- }
-
+ /* try to commit all transactions that haven't been commited yet on close
*/
if (f->txn) {
mdb_txn_commit(f->txn);
f->txn = NULL;
+ f->cursor = NULL;
Review Comment:
Thinking more about whether or not we should commit or rollback an existing
transaction in _close()..
Looking at where a ->txn != NULL can come from here:
1. After an _open() this allows to truncate if APR_DBM_RWTRUNC was set.
2. After a _store() and _del(), which do commit implicitly already, there is
nothing to commit in _close() (supposedly?)
3. After anything else there is nothing to commit either since they are read
operations (supposedly?)
So if mdb_txn_commit() does nothing for an "empty" ->tnx (`2.` and `3.`),
which seems likely, this commit in close only addresses `1.` right?
IOW, it avoids an implicit commit in _open() if APR_DBM_RWTRUNC is set,
defering to the next _store() or _del() or _close(), which looks fine/sensible.
In the other dbm drivers there does not seem to be any commit/rollback
possible or involved, _store() and _del() probably have immediate effect.
For now we get the same in lmdb with the implicit commits in _store() and
_del(), and I don't think we can avoid that since there is no commit/rollback
API in apr_dbm that the user can play with explicitely.
So, IIUC, unless we provide this new API (at some point) it seems that the
implicit commit in _close() is what we want, as the only possible optimization
with transactions for now...
Do I get this right?
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