Major - P3 Issue Status as of Apr 02, 2015
ISSUE SUMMARY
A mongod using the MMAPv1 storage engine may use too much memory to insert and remove documents with large indexed arrays.
USER IMPACT
MongoDB consumes an unnecessarily large amount of memory.
WORKAROUNDS
None.
AFFECTED VERSIONS
MongoDB 3.0.0 and 3.0.1 are affected by this issue.
FIX VERSION
The fix is included in the 3.0.2 production release.
Original description
Reproduce as follows:
db.c.ensureIndex({a:1})
doc = {a:[]}
for (var i=0; i<100000; i++)
doc.a.push(i)
db.c.insert(doc)
print('before:', db.serverStatus({tcmalloc:1}).tcmalloc.generic.heap_size/1024/1024, 'MB')
db.c.remove({})
print('after:', db.serverStatus({tcmalloc:1}).tcmalloc.generic.heap_size/1024/1024, 'MB')
Results:
3.0, mmapv1, 100k entries: before: 124.9453125 MB after: 3148.9453125 MB <=== 3.0, mmapv1, 50k entries: before: 93.234375 MB after: 1605.234375 MB <=== 3.0, wiredTiger, 100k entries: before: 72.28125 MB after: 98.53125 MB 2.6.8, mmapv1, 100k entries before: 79.4453125 MB after: 79.4453125 MB
- memory consumed is proportional to number of index entries, about 30 kB per entry
- issue is specific to mmapv1, does not occur with WT - so maybe issue is in the journal?
- problem does not occur in 2.6
