Re: Possibility of supporting snapshot in LMDB

To: Howard Chu <hyc@symas.com>

Subject: Re: Possibility of supporting snapshot in LMDB

From: Xinhai Kang <xinhaikang@gmail.com>

Date: Thu, 19 Nov 2015 17:39:12 -0800

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Thank you! I will check that.

On Thu, Nov 19, 2015 at 5:37 PM, Howard Chu <hyc@symas.com> wrote:

Xinhai Kang wrote:

Hi,

I am new to LMDB and I am checking the possibility of having persistent
snapshot support in LMDB.
In the current code, LMDB creates a transient snapshot when a transaction is
started. And also, LMDA supports multiple multiple databases in an
environment. I am wondering if it is possible to make the snapshot persistent
by storing the snapshot as a separate database (can different database share
pages? Or can multiple trees in the same database?).

I look forward to hearing from you! Or please kindly let me know if similar
feature has already been implemented somewhere.

That is not a feature that we need/want in LMDB. If you want persistent access to historical versions of a DB, use an append-only database. The btree.c written by Martin Hedenfalk would be one example.

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