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Re: lmdb - atomic actions
Tomer Doron wrote:
howard - thank you for the prompt reply and for putting this wonderful library
together.
to clarify my understanding, can you elaborate a little on the locking lmdb tx
provide cross threads and processes? in particular
1. do they provide a writer lock by default and one needs to flag
MDB_TXN_RDONLY when a writer lock is not required?
That is answered in the documentation.
2. given that mdb_txn_begin is a precursor to most other actions, are these
locks "data store" wide? is there some other mechanism to lock a key/value
pair or cursor so not to delay access to other keys? or is the basic
assumption such is unnecessary?
That is answered in the presentations.
thank again!
tomer
On Jul 24, 2013, at 1:52 PM, Howard Chu <hyc@symas.com <mailto:hyc@symas.com>>
wrote:
Tomer Doron wrote:
wondering what the best strategy to achieve atomic updates with LMDB.
what i am trying to achieve is a read then update atomic action given a
highly concurrent use case, for example, if a key/value pair represents a
counter, how does one increment or decrement the counter atomically.
i am pretty sure mdb_get -> mdv_set sequence is not atomic, wondering if
mdb_cursor_get -> mdv_cursor_put sequence is? perhaps a certain flag is
required on the get action to achieve a lock? in my bdb implementation i
used lockers to achieve this.
Transactions are atomic. Whatever operations you perform in a single
transaction will occur atomically. BDB-style locking is unnecessary.
--
-- Howard Chu
CTO, Symas Corp. http://www.symas.com
Director, Highland Sun http://highlandsun.com/hyc/
Chief Architect, OpenLDAP http://www.openldap.org/project/
--
-- Howard Chu
CTO, Symas Corp. http://www.symas.com
Director, Highland Sun http://highlandsun.com/hyc/
Chief Architect, OpenLDAP http://www.openldap.org/project/