Re: lmdb - atomic actions
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?
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?
thank again!
tomer
On Jul 24, 2013, at 1:52 PM, Howard Chu <hyc(a)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/
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