Shu, Xinxin wrote:
Hi list,
Recently I have integrated lmdb into ceph , got intial results , I dump all
records of lmdb, there are several different size key-value pairs,
1. key size : 45 byte, value size = 124 byte
2. key size : 85 byte, value size = 1187 byte
3. key size : 57 byte, value size = 135 byte
4. key size : 64 byte, value size = 182 byte
5. key size : 33 byte, value size = 4096 byte (used for real data, about 80 %)
this db contains about ~ 10000000 records, about 80 percent of records are the
last key-value pairs (key size 33 byte, value size 4096 byte), I calculate size
of all key-value pairs, about 33GB , but on-disk size is about 63GB, so space
amplification is ~ 2, is this amplification reasonable ? In which situation can
lmdb get such large space amplification? How can I reduce this amplification?
If you need any other details , please email me , any tips will be appreciate.
LMDB pages have a 16 byte header. In a system with 4096 byte pages, only
4080 bytes are available for user data, so storing a data value of 4096
bytes will use 2 pages.
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CTO, Symas Corp. http://www.symas.com
Director, Highland Sun http://highlandsun.com/hyc/
Chief Architect, OpenLDAP http://www.openldap.org/project/
