Compression of Mongodb on Netapp storage : strange reaction
Eric Franckx
we made some test on Mongodb to see how it reacts in our landscape.
We have install :
- Mongodb 2.6 rc1
- Suse Linux 11 SP3 64 bits in a VM with 4 CPU and 20 GB or RAM
- A NEtapp volume of 900 GB
- Create a collections with 1 billions docs with average size : 0.5KB
The collection had 1 billions docs and 2 or 3 index (included the default _id).
We have create one on some fields and each index was using between 19 and 30 GB.
db.a.stats()
{
"ns" : "pex.a",
"count" : 1000000000,
"size" : 496000000000,
"avgObjSize" : 496,
"storageSize" : 513716248896,
"numExtents" : 260,
"nindexes" : 5,
"lastExtentSize" : 2146426864,
"paddingFactor" : 1,
"systemFlags" : 0,
"userFlags" : 1,
"totalIndexSize" : 249163877984,
"indexSizes" : {
"_id_" : 32464467728,
"CustID_1_employeeid_1" : 78537625824,
"EventID_1" : 33235791568,
"Evtdate_1" : 27904459072,
"CustID_1" : 77021533792
},
"ok" : 1
}
db.stats()
{
"db" : "pex",
"collections" : 3,
"objects" : 1000000012,
"avgObjSize" : 495.99999507200005,
"dataSize" : 496000001024,
"storageSize" : 513716265280,
"numExtents" : 262,
"indexes" : 5,
"indexSize" : 249163877984,
"fileSize" : 774797000704,
"nsSizeMB" : 16,
"dataFileVersion" : {
"major" : 4,
"minor" : 5
},
"extentFreeList" : {
"num" : 0,
"totalSize" : 0
},
"ok" : 1
}
The complete database used 770GB on disk.
We have made a test : activate dedup on the Netapp volume. The win in space was not very great:
Then we made a test on compression on the volume level: and there the win was huge:
Very good ..
So now the performance impact, how react mongodb when we try a find ...
Surprise .... when I start the first find() --> normally on an indexed field, it was running, running .. then try to investigate a little:
db.a.getIndexes() --> no indexes anymore, strange ...
db.a.stats() --> oups only 79 millions docs where are my 1 billions docs ?????
db.a.count()
79547252
So to continue some test (and have update a Jira at Mongodb.com with the same info) I have create again :-( an index on a field ... take time to index 1 billions rows ... in fact 79 millions now
So start the command db.a.ensureIndex({EventID: 1}) and start the generation of the index ... wait to reach 100% for the 78 millions docs ... WAIT: it doesn't stop it continues ... 101% ... 1256% and continue and stop when : when it reach 1 billions rows ....
2014-04-02T08:48:36.017+0200 [conn1] Index Build: 79418500/79547252 99%
2014-04-02T08:48:39.014+0200 [conn1] Index Build: 79553000/79547252 100%
2014-04-02T08:48:51.548+0200 [conn1] Index Build: 79590800/79547252 100%
2014-04-02T08:48:54.012+0200 [conn1] Index Build: 79842700/79547252 100%
2014-04-02T08:48:57.013+0200 [conn1] Index Build: 80429000/79547252 101%
2014-04-02T08:49:09.099+0200 [conn1] Index Build: 80854100/79547252 101%
2014-04-02T08:49:12.014+0200 [conn1] Index Build: 81354900/79547252 102%
2014-04-02T21:27:47.443+0200 [conn1] Index Build: 999305900/79547252 1256%
2014-04-02T21:27:50.015+0200 [conn1] Index Build: 999672800/79547252 1256%
2014-04-02T21:28:20.017+0200 [conn1] Index: (2/3) BTree Bottom Up Progress: 1727800/1000000000 0%
2014-04-02T21:28:30.008+0200 [conn1] Index: (2/3) BTree Bottom Up Progress: 4027300/1000000000 0%
2014-04-02T21:28:40.280+0200 [conn1] Index: (2/3) BTree Bottom Up Progress: 6417700/1000000000 0%
Any idea ?
I think Mongodb is lost due to compression on storage level and use some Linux/OS command to compute some information.
Regards,
Eric
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