Jürgen Baier wrote:
Hi,
thanks for the answer. However, I still have a follow-up question on this
benchmark.
When I add 1 billion key/value pairs (16 byte MD5) to the LMDB database (in a
single transaction (but I also get similar results when I add the same data in
multiple transactions)) I get the following results:
Windows, without MDB_WRITEMAP: 46h
Windows, with MDB_WRITEMAP: 6h (!)
Linux (ext4), without MDB_WRITEMAP: 75h
Linux (ext4), with MDB_WRITEMAP: 73h
MDB_WRITEMAP seems to have a huge impact on write performance on Windows, but
on Linux I do not see similar improvements.
So I have two questions:
1) Could the the difference between Linux and Windows performance regarding
the MDB_WRITEMAP option be related to the fact that LMDB currently uses sparse
files on Linux, but not on Windows?
Unlikely.
2) Is there a way to speed up Linux? Is there a way to pre-allocate the
data.mdb on startup?
Try it and see. Use the env fd with fallocate(2).
Thanks,
Jürgen
On 21.11.17 21:17, Howard Chu wrote:
Jürgen Baier wrote:
Hi,
I have a question about LMDB (I hope this is the right mailing list for
such a question).
I'm running a benchmark (which is similar to my intended use case) which
does not behave as I hoped. I store 1 billion key/value pairs in a single
LMDB database. _In a single transaction._ The keys are MD5 hash codes from
random data (16 bytes) and the value is the string "test".
The documentation about mdb_page_spill says (as far as I understand) that
this function is called to prevent MDB_TXN_FULL situations. Does this mean
that my transaction is simply too large to be handled efficiently by LMDB?
Yes.
--
-- Howard Chu
CTO, Symas Corp. http://www.symas.com
Director, Highland Sun http://highlandsun.com/hyc/
Chief Architect, OpenLDAP http://www.openldap.org/project/
