9:08 a.m.
Hello,
this might be a trivial question for you but I didn't find anything in the
documentation nor any mention in the examples.
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?
I'm running a stress test and didn't spot any issues so far. Though I might
be extremely lucky today.
The DB is used in multi-threaded environment but the code illustrated above
is protected with a mutex.
I tried to dig a bit into the lmdb internals but unfortunately didn't get
any glue.
Thanks for your help,
Dmytro
10:36 a.m.
Dmytro Milinevskyy wrote:
Hello,
this might be a trivial question for you but I didn't find anything in the
documentation nor any mention in the examples.
Which examples did you look at? mtest.c (and others) all operate this way already.
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.
--
-- Howard Chu
CTO, Symas Corp. http://www.symas.com
Director, Highland Sun http://highlandsun.com/hyc/
Chief Architect, OpenLDAP http://www.openldap.org/project/
2:03 p.m.
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.
8:39 a.m.
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
> > 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.
What exactly does a subsequent update operation mean? Overwriting the
value of the same key, or any mdb_put or mdb_cursor_put operation at
all, regardless of which key they touch?
9:05 a.m.
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
>>> 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.
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
is Yes.
> 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.
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/
9:23 a.m.
On Tue, 2015-05-19 at 17:05 +0100, Howard Chu wrote:
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
> > > > 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.
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
is Yes.
> > 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.
> 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.
Okay, thanks for the clarification!
> or any mdb_put or mdb_cursor_put operation at
> all, regardless of which key they touch?
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5 comments
4 participants
participants (4)
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Dmytro Milinevskyy -
Hallvard Breien Furuseth -
Howard Chu -
Timur Kristóf