[Date Prev][Date Next] [Chronological] [Thread] [Top]

Re: mdb_dbi_open and threads

Thanks for clarifying.
I did get the impression but there was some part of it where I thought the doc was not clear enough.
Thanks anyway.

On Sat, May 20, 2017 at 10:46 PM, Howard Chu <hyc@symas.com> wrote:
Muhammed Muneer wrote:
Is the following  valid.

1) Read transaction 1 is started
2) Read transaction 2 is started and calls mdb_dbi_open and commits
3) Read transaction 1 uses the handle from (2)

 Please learn how to read. The doc says more than you quoted before, and it already quite explicitly defines its properties:

http://www.lmdb.tech/doc/group__internal.html#gac08cad5b096925642ca359a6d6f0562a

        The database handle will be private to the current transaction until the transaction is successfully committed. If the transaction is aborted the handle will be closed automatically. After a successful commit the handle will reside in the shared environment, and may be used by other transactions.

In your question above, transaction 1 is not after transaction 2 therefore it cannot use the handle that transaction 2 commits.

The handle does not exist in the shared environment until after its opening transaction commits. If it doesn't exist in the shared environment when a transaction begins, then it is not visible or valid in that particular transaction.

Just follow the recommendation to open all handles at the beginning of the program.


On Sat, May 20, 2017 at 6:46 PM, Muhammed Muneer <elendilm@gmail.com
 <mailto:elendilm@gmail.com>> wrote:

    Thanks.

    On Sat, May 20, 2017 at 6:29 PM, Klaus Malorny <Klaus.Malorny@knipp.de
     <mailto:Klaus.Malorny@knipp.de>> wrote:

        On 5/20/17 2:02 PM, Muhammed Muneer wrote:

            So when the doc says

                  * The database handle will be private to the current
            transaction until
                  * the transaction is successfully committed.

            "the handle being private" only refers to the first mdb_dbi_open.
            Once this transaction is committed, one doesn't have to call this
            again in subsequent concurrent transactions and can use this handle.
            And then this handle won't be private at all.

            Did I get it right?


        Yes. I do this exactly that way as part of my initial setup of my
        application. Once the transaction is committed, I use the returned
        handles setup from whatever thread that needs to access the respective
        database. I never call mdb_dbi_open again after the setup.

        Regards,

        Klaus





--
  -- Howard Chu
  CTO, Symas Corp.           http://www.symas.com
  Director, Highland Sun     http://highlandsun.com/hyc/
  Chief Architect, OpenLDAP  http://www.openldap.org/project/