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Re: lmdb: is read operation permitted inside the write transaction?
Timur Kristóf wrote:
On Mon, 2015-05-18 at 23:03 +0200, Hallvard Breien Furuseth wrote:
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
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)
Will it be always valid data?
...No. I expect he means v = the MDB_val returned by mdb_get().
mdb_put() can modify the data it points at.
Since he's using "v+1" in his example I assumed he's making a local copy of
the returned values. Anyway, the plain answer to the question in the Subject
See the MDB_val documentation in ldmb.h:
* Values returned from the database are valid only until a
* update operation, or the end of the transaction. Do not modify or
* free them, they commonly point into the database itself.
What exactly does a subsequent update operation mean? Overwriting the
value of the same key,
If we meant "same key" we would have said so.
or any mdb_put or mdb_cursor_put operation at
all, regardless of which key they touch?
-- Howard Chu
CTO, Symas Corp. http://www.symas.com
Director, Highland Sun http://highlandsun.com/hyc/
Chief Architect, OpenLDAP http://www.openldap.org/project/