SECONDARY> db.somecoll.stats()
{
  "ns" : "dbdoc.somecoll",
  "count" : 221435,
  "size" : 29477552228,
  "avgObjSize" : 133120,
  "storageSize" : 107902332928,
  "capped" : false,
  "wiredTiger" : {
    "metadata" : {
      "formatVersion" : 1
    },
    "creationString" : "access_pattern_hint=none,allocation_size=4KB,app_metadata=(formatVersion=1),block_allocation=best,block_compressor=snappy,cache_resident=false,checksum=on,colgroups=,collator=,columns=,dictionary=0,encryption=(keyid=,name=),exclusive=false,extractor=,format=btree,huffman_key=,huffman_value=,ignore_in_memory_cache_size=false,immutable=false,internal_item_max=0,internal_key_max=0,internal_key_truncate=true,internal_page_max=4KB,key_format=q,key_gap=10,leaf_item_max=0,leaf_key_max=0,leaf_page_max=32KB,leaf_value_max=64MB,log=(enabled=true),lsm=(auto_throttle=true,bloom=true,bloom_bit_count=16,bloom_config=,bloom_hash_count=8,bloom_oldest=false,chunk_count_limit=0,chunk_max=5GB,chunk_size=10MB,merge_max=15,merge_min=0),memory_page_max=10m,os_cache_dirty_max=0,os_cache_max=0,prefix_compression=false,prefix_compression_min=4,source=,split_deepen_min_child=0,split_deepen_per_child=0,split_pct=90,type=file,value_format=u",
    "type" : "file",
    "uri" : "statistics:table:dbdoc/collection-78--3418042999270868539",
    "LSM" : {
      "bloom filter false positives" : 0,
      "bloom filter hits" : 0,
      "bloom filter misses" : 0,
      "bloom filter pages evicted from cache" : 0,
      "bloom filter pages read into cache" : 0,
      "bloom filters in the LSM tree" : 0,
      "chunks in the LSM tree" : 0,
      "highest merge generation in the LSM tree" : 0,
      "queries that could have benefited from a Bloom filter that did not exist" : 0,
      "sleep for LSM checkpoint throttle" : 0,
      "sleep for LSM merge throttle" : 0,
      "total size of bloom filters" : 0
    },
    "block-manager" : {
      "allocations requiring file extension" : 0,
      "blocks allocated" : 0,
      "blocks freed" : 0,
      "checkpoint size" : 29916192768,
      "file allocation unit size" : 4096,
      "file bytes available for reuse" : 8498855936,
      "file magic number" : 120897,
      "file major version number" : 1,
      "file size in bytes" : 107902332928,
      "minor version number" : 0
    },
    "btree" : {
      "btree checkpoint generation" : 0,
      "column-store fixed-size leaf pages" : 0,
      "column-store internal pages" : 0,
      "column-store variable-size RLE encoded values" : 0,
      "column-store variable-size deleted values" : 0,
      "column-store variable-size leaf pages" : 0,
      "fixed-record size" : 0,
      "maximum internal page key size" : 368,
      "maximum internal page size" : 4096,
      "maximum leaf page key size" : 2867,
      "maximum leaf page size" : 32768,
      "maximum leaf page value size" : 67108864,
      "maximum tree depth" : 0,
      "number of key/value pairs" : 0,
      "overflow pages" : 0,
      "pages rewritten by compaction" : 0,
      "row-store internal pages" : 0,
      "row-store leaf pages" : 0
    },
    "cache" : {
      "bytes currently in the cache" : 213732,
      "bytes read into cache" : 176748,
      "bytes written from cache" : 0,
      "checkpoint blocked page eviction" : 0,
      "data source pages selected for eviction unable to be evicted" : 0,
      "hazard pointer blocked page eviction" : 0,
      "in-memory page passed criteria to be split" : 0,
      "in-memory page splits" : 0,
      "internal pages evicted" : 0,
      "internal pages split during eviction" : 0,
      "leaf pages split during eviction" : 0,
      "modified pages evicted" : 0,
      "overflow pages read into cache" : 0,
      "overflow values cached in memory" : 0,
      "page split during eviction deepened the tree" : 0,
      "page written requiring lookaside records" : 0,
      "pages read into cache" : 4,
      "pages read into cache requiring lookaside entries" : 0,
      "pages requested from the cache" : 3,
      "pages written from cache" : 0,
      "pages written requiring in-memory restoration" : 0,
      "tracked dirty bytes in the cache" : 0,
      "unmodified pages evicted" : 0
    },
    "cache_walk" : {
      "Average difference between current eviction generation when the page was last considered" : 0,
      "Average on-disk page image size seen" : 0,
      "Clean pages currently in cache" : 0,
      "Current eviction generation" : 0,
      "Dirty pages currently in cache" : 0,
      "Entries in the root page" : 0,
      "Internal pages currently in cache" : 0,
      "Leaf pages currently in cache" : 0,
      "Maximum difference between current eviction generation when the page was last considered" : 0,
      "Maximum page size seen" : 0,
      "Minimum on-disk page image size seen" : 0,
      "On-disk page image sizes smaller than a single allocation unit" : 0,
      "Pages created in memory and never written" : 0,
      "Pages currently queued for eviction" : 0,
      "Pages that could not be queued for eviction" : 0,
      "Refs skipped during cache traversal" : 0,
      "Size of the root page" : 0,
      "Total number of pages currently in cache" : 0
    },
    "compression" : {
      "compressed pages read" : 0,
      "compressed pages written" : 0,
      "page written failed to compress" : 0,
      "page written was too small to compress" : 0,
      "raw compression call failed, additional data available" : 0,
      "raw compression call failed, no additional data available" : 0,
      "raw compression call succeeded" : 0
    },
    "cursor" : {
      "bulk-loaded cursor-insert calls" : 0,
      "create calls" : 1,
      "cursor-insert key and value bytes inserted" : 0,
      "cursor-remove key bytes removed" : 0,
      "cursor-update value bytes updated" : 0,
      "insert calls" : 0,
      "next calls" : 0,
      "prev calls" : 1,
      "remove calls" : 0,
      "reset calls" : 1,
      "restarted searches" : 0,
      "search calls" : 0,
      "search near calls" : 0,
      "truncate calls" : 0,
      "update calls" : 0
    },
    "reconciliation" : {
      "dictionary matches" : 0,
      "fast-path pages deleted" : 0,
      "internal page key bytes discarded using suffix compression" : 0,
      "internal page multi-block writes" : 0,
      "internal-page overflow keys" : 0,
      "leaf page key bytes discarded using prefix compression" : 0,
      "leaf page multi-block writes" : 0,
      "leaf-page overflow keys" : 0,
      "maximum blocks required for a page" : 0,
      "overflow values written" : 0,
      "page checksum matches" : 0,
      "page reconciliation calls" : 0,
      "page reconciliation calls for eviction" : 0,
      "pages deleted" : 0
    },
    "session" : {
      "object compaction" : 0,
      "open cursor count" : 1
    },
    "transaction" : {
      "update conflicts" : 0
    }
  }

2018-07-06T13:01:53.316+0800 I REPL [ReplicationExecutor] going into maintenance mode with 0 other maintenance mode tasks in progress 2018-07-06T13:01:53.316+0800 I REPL [ReplicationExecutor] transition to RECOVERING 2018-07-06T13:01:53.316+0800 I COMMAND [conn4] compact dbdoc.somecoll begin, options: paddingMode: NONE validateDocuments: 1 2018-07-06T13:01:53.367+0800 I ACCESS [conn12] Successfully authenticated as principal __cloud_internal on admin 2018-07-06T13:01:53.375+0800 I STORAGE [conn4] WiredTiger [1530853313:375677][21031:0x7effc9e7c700], file:dbdoc/collection-78--3418042999270868539.wt, WT_SESSION.compact: ============ testing for compaction 2018-07-06T13:01:53.375+0800 I STORAGE [conn4] WiredTiger [1530853313:375742][21031:0x7effc9e7c700], file:dbdoc/collection-78--3418042999270868539.wt, WT_SESSION.compact: file size 102903MB (107902332928) with 7% space available 8105MB (8498855936) 2018-07-06T13:01:53.467+0800 I NETWORK [conn12] end connection 127.0.0.1:44591 (6 connections now open) 2018-07-06T13:01:53.467+0800 I NETWORK [conn11] end connection 127.0.0.1:44582 (6 connections now open) 2018-07-06T13:01:53.764+0800 I STORAGE [conn4] WiredTiger [1530853313:764520][21031:0x7effc9e7c700], file:dbdoc/collection-78--3418042999270868539.wt, WT_SESSION.compact: 0%: 3MB, (3489792B, 0%) 2018-07-06T13:01:53.764+0800 I STORAGE [conn4] WiredTiger [1530853313:764587][21031:0x7effc9e7c700], file:dbdoc/collection-78--3418042999270868539.wt, WT_SESSION.compact: 10%: 2204MB, (2311172096B, 27%) 2018-07-06T13:01:53.764+0800 I STORAGE [conn4] WiredTiger [1530853313:764603][21031:0x7effc9e7c700], file:dbdoc/collection-78--3418042999270868539.wt, WT_SESSION.compact: 20%: 1580MB, (1657495552B, 19%) 2018-07-06T13:01:53.764+0800 I STORAGE [conn4] WiredTiger [1530853313:764615][21031:0x7effc9e7c700], file:dbdoc/collection-78--3418042999270868539.wt, WT_SESSION.compact: 30%: 1539MB, (1614770176B, 18%) 2018-07-06T13:01:53.764+0800 I STORAGE [conn4] WiredTiger [1530853313:764627][21031:0x7effc9e7c700], file:dbdoc/collection-78--3418042999270868539.wt, WT_SESSION.compact: 40%: 692MB, (726429696B, 8%) 2018-07-06T13:01:53.764+0800 I STORAGE [conn4] WiredTiger [1530853313:764665][21031:0x7effc9e7c700], file:dbdoc/collection-78--3418042999270868539.wt, WT_SESSION.compact: 50%: 824MB, (864960512B, 10%) 2018-07-06T13:01:53.764+0800 I STORAGE [conn4] WiredTiger [1530853313:764678][21031:0x7effc9e7c700], file:dbdoc/collection-78--3418042999270868539.wt, WT_SESSION.compact: 60%: 444MB, (465973248B, 5%) 2018-07-06T13:01:53.764+0800 I STORAGE [conn4] WiredTiger [1530853313:764690][21031:0x7effc9e7c700], file:dbdoc/collection-78--3418042999270868539.wt, WT_SESSION.compact: 70%: 12MB, (12582912B, 0%)2018-07-06T13:01:53.764+0800 I STORAGE [conn4] WiredTiger [1530853313:764702][21031:0x7effc9e7c700], file:dbdoc/collection-78--3418042999270868539.wt, WT_SESSION.compact: 80%: 9MB, (10027008B, 0%)
2018-07-06T13:01:53.764+0800 I STORAGE [conn4] WiredTiger [1530853313:764714][21031:0x7effc9e7c700], file:dbdoc/collection-78--3418042999270868539.wt, WT_SESSION.compact: 90%: 793MB, (831954944B, 9%)
265911 2018-07-06T13:01:53.764+0800 I STORAGE [conn4] WiredTiger [1530853313:764775][21031:0x7effc9e7c700], file:dbdoc/collection-78--3418042999270868539.wt, WT_SESSION.compact: dbdoc/collection-78--3418042999270868539.wt: 7302MB (7656873984) available space in the first 80% of the file
2018-07-06T13:01:53.764+0800 I STORAGE [conn4] WiredTiger [1530853313:764796][21031:0x7effc9e7c700], file:dbdoc/collection-78--3418042999270868539.wt, WT_SESSION.compact: dbdoc/collection-78--3418042999270868539.wt: 7311MB (7666900992) available space in the first 90% of the file
2018-07-06T13:01:53.764+0800 I STORAGE [conn4] WiredTiger [1530853313:764808][21031:0x7effc9e7c700], file:dbdoc/collection-78--3418042999270868539.wt, WT_SESSION.compact: dbdoc/collection-78--3418042999270868539.wt: require 10% or 10290MB (10790233292) in the first 90% of the file to perform compaction , compaction skipped
2018-07-06T13:01:53.764+0800 I STORAGE [conn4] WiredTiger [1530853313:764825][21031:0x7effc9e7c700], file:dbdoc/collection-78--3418042999270868539.wt, WT_SESSION.compact: ============ ending compaction pass
2018-07-06T13:01:53.764+0800 I STORAGE [conn4] WiredTiger [1530853313:764837][21031:0x7effc9e7c700], file:dbdoc/collection-78--3418042999270868539.wt, WT_SESSION.compact: pages reviewed: 0
265916 2018-07-06T13:01:53.764+0800 I STORAGE [conn4] WiredTiger [1530853313:764850][21031:0x7effc9e7c700], file:dbdoc/collection-78--3418042999270868539.wt, WT_SESSION.compact: pages skipped: 0
265917 2018-07-06T13:01:53.764+0800 I STORAGE [conn4] WiredTiger [1530853313:764861][21031:0x7effc9e7c700], file:dbdoc/collection-78--3418042999270868539.wt, WT_SESSION.compact: pages written: 0