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Re: FW: questions about LMDB

To: "Shu, Xinxin" <xinxin.shu@intel.com>, "openldap-technical@openldap.org" <openldap-technical@openldap.org>
Subject: Re: FW: questions about LMDB
From: Howard Chu <hyc@symas.com>
Date: Fri, 20 Mar 2015 05:01:34 +0000
In-reply-to: <75674D092A819E4189E91166C74CB90D0150C160@shsmsx102.ccr.corp.intel.com>
References: <75674D092A819E4189E91166C74CB90D0150AE65@shsmsx102.ccr.corp.intel.com> <75674D092A819E4189E91166C74CB90D0150AF0A@shsmsx102.ccr.corp.intel.com> <550AF08A.1070709@symas.com> <75674D092A819E4189E91166C74CB90D0150B11C@shsmsx102.ccr.corp.intel.com> <75674D092A819E4189E91166C74CB90D0150C160@shsmsx102.ccr.corp.intel.com>
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Shu, Xinxin wrote:

CC  technical list

Shu, Xinxin wrote:

Several other questions about lmdb

1) does lmdb store one key-value pair in a single page?


Usually, yes, a key-value pair must fit in a single page. This is already documented.

http://symas.com/mdb/doc/group__mdb.html#gaaf0be004f33828bf2fb09d77eb3cef94

How lmdb organizes these key-value pairs in a single page


Not documented. You can read the explanation in the source code. It will not be documented elsewhere since implementation details like this aren't relevant to users, and DB internal formats are subject to change.

2)  if size is larger than single page size , how lmdb process this request?


Like all B+tree databases, it uses overflow pages.

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

References:
- FW: questions about LMDB
  - From: "Shu, Xinxin" <xinxin.shu@intel.com>

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