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Re: Possibility of supporting snapshot in LMDB

To: Xinhai Kang <xinhaikang@gmail.com>, openldap-devel@openldap.org
Subject: Re: Possibility of supporting snapshot in LMDB
From: Howard Chu <hyc@symas.com>
Date: Fri, 20 Nov 2015 01:37:08 +0000
In-reply-to: <CAEe0cP4pK1+PPk+hbrF3LnMuw4p+kh=DCJeFaPsZJNs+TxEUxw@mail.gmail.com>
References: <CAEe0cP4pK1+PPk+hbrF3LnMuw4p+kh=DCJeFaPsZJNs+TxEUxw@mail.gmail.com>
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:41.0) Gecko/20100101 Firefox/41.0 SeaMonkey/2.38a1

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 accessto historical versions of a DB, use an append-only database. The btree.cwritten 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/

Follow-Ups:
- Re: Possibility of supporting snapshot in LMDB
  - From: Xinhai Kang <xinhaikang@gmail.com>

References:
- Possibility of supporting snapshot in LMDB
  - From: Xinhai Kang <xinhaikang@gmail.com>

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