Re: lmdb: is read operation permitted inside the write transaction?

On 12/05/15 19:36, Howard Chu wrote:

Dmytro Milinevskyy wrote:

...

Basically I need to have an opportunity to call mdb_get while in write transaction. The sequence is smth like:

• txn = mdb_txn_begin(flags=0)

for i in 0..x: - v = mdb_get(txn, i) - mdb_put(txn, x+i, v) - mdb_put(txn, i, v+1)

• mdb_txn_commit(txn)

Will it be always valid data?

Yes.

...No. I expect he means v = the MDB_val returned by mdb_get(). mdb_put() can modify the data it points at.

See the MDB_val documentation in ldmb.h: * Values returned from the database are valid only until a subsequent * update operation, or the end of the transaction. Do not modify or * free them, they commonly point into the database itself.