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Re: [lmdb] MDB_BAD_DBI error upon mdb_txn_commit (newbie question)

hlaw wrote:

Thank you!

It appears that mdb_dbi_open() must be called before any read / write
access to a database in a transaction,


True.


and all read / write have to be
done in a transaction?


True.


If this is the case, is it correct that due to
the concurrency restriction above, there is essentially no concurrent
access (including read and write) to the same database in a
multi-threaded process,


False.


since a database is available to one transaction
in a time?


False. Reread the mdb_dbi_open doc. http://symas.com/mdb/doc/group__mdb.html#gac08cad5b096925642ca359a6d6f0562a



2015-03-30 19:52 GMT+08:00 Hallvard Breien Furuseth
<h.b.furuseth@usit.uio.no <mailto:h.b.furuseth@usit.uio.no>>:

    You're abusing mdb_dbi_open().  Its doc says:

       "This function must not be called from multiple concurrent
       transactions in the same process. A transaction that uses this
       function must finish (either commit or abort) before any other
       transaction in the process may use this function."

    That text could have stood out a bit better in the doc:-(

    The error is simple for lmdb to try to catch, though without
    locking it cannot guarantee to catch it.  Try this patch:
    <http://folk.uio.no/hbf/__OpenLDAP/mdb.serial-open.diff
    <http://folk.uio.no/hbf/OpenLDAP/mdb.serial-open.diff>>

    (Howard, this is branch "mdb/serial-open" in my UiO repo.)
    Not sure if it should do more than this.  E.g. attack mdb_drop
    too.  Maybe set MDB_TXN_ERROR since a program with broken
    threading can break the DB.

    --
    Hallvard





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