test> db.test1.find({}).sort({ts: -1}).limit(1).explain()
{
  explainVersion: '1',
  stages: [
    {
      '$cursor': {
        queryPlanner: {
          namespace: 'test.system.buckets.test1',
          indexFilterSet: false,
          parsedQuery: {},
          queryHash: '8B3D4AB8',
          planCacheKey: 'D542626C',
          maxIndexedOrSolutionsReached: false,
          maxIndexedAndSolutionsReached: false,
          maxScansToExplodeReached: false,
          winningPlan: { stage: 'COLLSCAN', direction: 'forward' },
          rejectedPlans: []
        },
        executionStats: {
          executionSuccess: true,
          nReturned: 979611,
          executionTimeMillis: 1560,
          totalKeysExamined: 0,
          totalDocsExamined: 979611,
          executionStages: {
            stage: 'COLLSCAN',
            nReturned: 979611,
            executionTimeMillisEstimate: 40,
            works: 979613,
            advanced: 979611,
            needTime: 1,
            needYield: 0,
            saveState: 1123,
            restoreState: 1123,
            isEOF: 1,
            direction: 'forward',
            docsExamined: 979611
          },
          allPlansExecution: []
        }
      },
      nReturned: Long("979611"),
      executionTimeMillisEstimate: Long("1002")
    },
    {
      '$_internalUnpackBucket': {
        exclude: [],
        timeField: 'ts',
        metaField: 'md',
        bucketMaxSpanSeconds: 3600
      },
      nReturned: Long("1000000"),
      executionTimeMillisEstimate: Long("1487")
    },
    {
      '$sort': { sortKey: { ts: -1 }, limit: Long("1") },
      totalDataSizeSortedBytesEstimate: Long("0"),
      usedDisk: false,
      nReturned: Long("1"),
      executionTimeMillisEstimate: Long("1559")
    }
  ],
  serverInfo: {
    host: 'aqua-db',
    port: 27017,
    version: '5.0.5',
    gitVersion: 'd65fd89df3fc039b5c55933c0f71d647a54510ae'
  },
  serverParameters: {
    internalQueryFacetBufferSizeBytes: 104857600,
    internalQueryFacetMaxOutputDocSizeBytes: 104857600,
    internalLookupStageIntermediateDocumentMaxSizeBytes: 104857600,
    internalDocumentSourceGroupMaxMemoryBytes: 104857600,
    internalQueryMaxBlockingSortMemoryUsageBytes: 104857600,
    internalQueryProhibitBlockingMergeOnMongoS: 0,
    internalQueryMaxAddToSetBytes: 104857600,
    internalDocumentSourceSetWindowFieldsMaxMemoryBytes: 104857600
  },
  command: {
    aggregate: 'system.buckets.test1',
    pipeline: [
      {
        '$_internalUnpackBucket': {
          timeField: 'ts',
          metaField: 'md',
          bucketMaxSpanSeconds: 3600,
          exclude: []
        }
      },
      { '$sort': { ts: -1 } },
      { '$limit': Long("1") }
    ],
    cursor: {},
    collation: { locale: 'simple' }
  },
  ok: 1
}
test> db.test1.stats()
{
  ns: 'test.test1',
  size: 242718310,
  timeseries: {
    bucketsNs: 'test.system.buckets.test1',
    bucketCount: 979611,
    avgBucketSize: 247,
    numBucketInserts: 979611,
    numBucketUpdates: 30,
    numBucketsOpenedDueToMetadata: 1,
    numBucketsClosedDueToCount: 0,
    numBucketsClosedDueToSize: 0,
    numBucketsClosedDueToTimeForward: 480653,
    numBucketsClosedDueToTimeBackward: 498957,
    numBucketsClosedDueToMemoryThreshold: 0,
    numCommits: 979641,
    numWaits: 0,
    numMeasurementsCommitted: 1000000,
    avgNumMeasurementsPerCommit: 1
  },
  storageSize: 77029376,
  freeStorageSize: 38363136,
  capped: false,
  wiredTiger: {
    metadata: { formatVersion: 1 },
    creationString: 'access_pattern_hint=none,allocation_size=4KB,app_metadata=(formatVersion=1),assert=(commit_timestamp=none,durable_timestamp=none,read_timestamp=none,write_timestamp=off),block_allocation=best,block_compressor=zstd,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,import=(enabled=false,file_metadata=,repair=false),internal_item_max=0,internal_key_max=0,internal_key_truncate=true,internal_page_max=4KB,key_format=u,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_custom=(prefix=,start_generation=0,suffix=),merge_max=15,merge_min=0),memory_page_image_max=0,memory_page_max=10m,os_cache_dirty_max=0,os_cache_max=0,prefix_compression=false,prefix_compression_min=4,readonly=false,source=,split_deepen_min_child=0,split_deepen_per_child=0,split_pct=90,tiered_object=false,tiered_storage=(auth_token=,bucket=,bucket_prefix=,cache_directory=,local_retention=300,name=,object_target_size=10M),type=file,value_format=u,verbose=[],write_timestamp_usage=none',
    type: 'file',
    uri: 'statistics:table:collection-0-615623608163548620',
    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': 5091,
      'blocks allocated': 364058,
      'blocks freed': 361124,
      'checkpoint size': 38645760,
      'file allocation unit size': 4096,
      'file bytes available for reuse': 38363136,
      'file magic number': 120897,
      'file major version number': 1,
      'file size in bytes': 77029376,
      'minor version number': 0
    },
    btree: {
      'btree checkpoint generation': 28,
      'btree clean tree checkpoint expiration time': Long("9223372036854775807"),
      'btree compact pages reviewed': 0,
      'btree compact pages rewritten': 0,
      'btree compact pages skipped': 0,
      'btree skipped by compaction as process would not reduce size': 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 size': 4096,
      'maximum leaf page key size': 2867,
      'maximum leaf page size': 32768,
      'maximum leaf page value size': 67108864,
      'maximum tree depth': 3,
      'number of key/value pairs': 0,
      'overflow pages': 0,
      'row-store empty values': 0,
      'row-store internal pages': 0,
      'row-store leaf pages': 0
    },
    cache: {
      'bytes currently in the cache': 278016709,
      'bytes dirty in the cache cumulative': Long("72305928370"),
      'bytes read into cache': Long("31436761817"),
      'bytes written from cache': Long("33005096700"),
      'checkpoint blocked page eviction': 2598,
      'checkpoint of history store file blocked non-history store page eviction': 0,
      'data source pages selected for eviction unable to be evicted': 3076,
      'eviction gave up due to detecting an out of order on disk value behind the last update on the chain': 0,
      'eviction gave up due to detecting an out of order tombstone ahead of the selected on disk update': 0,
      'eviction gave up due to detecting an out of order tombstone ahead of the selected on disk update after validating the update chain': 0,
      'eviction gave up due to detecting out of order timestamps on the update chain after the selected on disk update': 0,
      'eviction walk passes of a file': 326501,
      'eviction walk target pages histogram - 0-9': 15726,
      'eviction walk target pages histogram - 10-31': 35406,
      'eviction walk target pages histogram - 128 and higher': 0,
      'eviction walk target pages histogram - 32-63': 54257,
      'eviction walk target pages histogram - 64-128': 221112,
      'eviction walk target pages reduced due to history store cache pressure': 0,
      'eviction walks abandoned': 9,
      'eviction walks gave up because they restarted their walk twice': 10049,
      'eviction walks gave up because they saw too many pages and found no candidates': 393,
      'eviction walks gave up because they saw too many pages and found too few candidates': 32,
      'eviction walks reached end of tree': 89921,
      'eviction walks restarted': 0,
      'eviction walks started from root of tree': 10799,
      'eviction walks started from saved location in tree': 315702,
      'hazard pointer blocked page eviction': 478,
      'history store table insert calls': 0,
      'history store table insert calls that returned restart': 0,
      'history store table out-of-order resolved updates that lose their durable timestamp': 0,
      'history store table out-of-order updates that were fixed up by reinserting with the fixed timestamp': 0,
      'history store table reads': 0,
      'history store table reads missed': 0,
      'history store table reads requiring squashed modifies': 0,
      'history store table truncation by rollback to stable to remove an unstable update': 0,
      'history store table truncation by rollback to stable to remove an update': 0,
      'history store table truncation to remove an update': 0,
      'history store table truncation to remove range of updates due to key being removed from the data page during reconciliation': 0,
      'history store table truncation to remove range of updates due to out-of-order timestamp update on data page': 0,
      'history store table writes requiring squashed modifies': 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': 2826,
      'modified pages evicted': 677223,
      'overflow pages read into cache': 0,
      'page split during eviction deepened the tree': 0,
      'page written requiring history store records': 0,
      'pages read into cache': 346668,
      'pages read into cache after truncate': 1,
      'pages read into cache after truncate in prepare state': 0,
      'pages requested from the cache': 1027047,
      'pages seen by eviction walk': 67904709,
      'pages written from cache': 364036,
      'pages written requiring in-memory restoration': 333782,
      'the number of times full update inserted to history store': 0,
      'the number of times reverse modify inserted to history store': 0,
      'tracked dirty bytes in the cache': 0,
      'unmodified pages evicted': 1139
    },
    cache_walk: {
      'Average difference between current eviction generation when the page was last considered': 0,
      'Average on-disk page image size seen': 0,
      'Average time in cache for pages that have been visited by the eviction server': 0,
      'Average time in cache for pages that have not been visited by the eviction server': 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,
      'Number of pages never visited by eviction server': 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
    },
    'checkpoint-cleanup': {
      'pages added for eviction': 0,
      'pages removed': 0,
      'pages skipped during tree walk': 1516,
      'pages visited': 21581
    },
    compression: {
      'compressed page maximum internal page size prior to compression': 4096,
      'compressed page maximum leaf page size prior to compression ': 131072,
      'compressed pages read': 346668,
      'compressed pages written': 363873,
      'number of blocks with compress ratio greater than 64': 0,
      'number of blocks with compress ratio smaller than 16': 3451,
      'number of blocks with compress ratio smaller than 2': 0,
      'number of blocks with compress ratio smaller than 32': 0,
      'number of blocks with compress ratio smaller than 4': 0,
      'number of blocks with compress ratio smaller than 64': 0,
      'number of blocks with compress ratio smaller than 8': 343217,
      'page written failed to compress': 0,
      'page written was too small to compress': 163
    },
    cursor: {
      'Total number of entries skipped by cursor next calls': 3775,
      'Total number of entries skipped by cursor prev calls': 0,
      'Total number of entries skipped to position the history store cursor': 0,
      'Total number of times a search near has exited due to prefix config': 0,
      'bulk loaded cursor insert calls': 0,
      'cache cursors reuse count': 1142,
      'close calls that result in cache': 1145,
      'create calls': 3,
      'cursor next calls that skip due to a globally visible history store tombstone': 0,
      'cursor next calls that skip greater than or equal to 100 entries': 0,
      'cursor next calls that skip less than 100 entries': 8118637,
      'cursor prev calls that skip due to a globally visible history store tombstone': 0,
      'cursor prev calls that skip greater than or equal to 100 entries': 0,
      'cursor prev calls that skip less than 100 entries': 0,
      'insert calls': 979641,
      'insert key and value bytes': 255461090,
      modify: 0,
      'modify key and value bytes affected': 0,
      'modify value bytes modified': 0,
      'next calls': 8118637,
      'open cursor count': 0,
      'operation restarted': 0,
      'prev calls': 0,
      'remove calls': 0,
      'remove key bytes removed': 0,
      'reserve calls': 0,
      'reset calls': 11550,
      'search calls': 60,
      'search history store calls': 0,
      'search near calls': 9228,
      'truncate calls': 0,
      'update calls': 0,
      'update key and value bytes': 0,
      'update value size change': 0
    },
    reconciliation: {
      'approximate byte size of timestamps in pages written': 0,
      'approximate byte size of transaction IDs in pages written': 12072,
      'dictionary matches': 0,
      'fast-path pages deleted': 0,
      'internal page key bytes discarded using suffix compression': 1584831,
      'internal page multi-block writes': 11,
      'leaf page key bytes discarded using prefix compression': 0,
      'leaf page multi-block writes': 2866,
      'leaf-page overflow keys': 0,
      'maximum blocks required for a page': 1,
      'overflow values written': 0,
      'page checksum matches': 0,
      'page reconciliation calls': 684434,
      'page reconciliation calls for eviction': 677027,
      'pages deleted': 0,
      'pages written including an aggregated newest start durable timestamp ': 0,
      'pages written including an aggregated newest stop durable timestamp ': 0,
      'pages written including an aggregated newest stop timestamp ': 0,
      'pages written including an aggregated newest stop transaction ID': 0,
      'pages written including an aggregated newest transaction ID ': 148,
      'pages written including an aggregated oldest start timestamp ': 0,
      'pages written including an aggregated prepare': 0,
      'pages written including at least one prepare': 0,
      'pages written including at least one start durable timestamp': 0,
      'pages written including at least one start timestamp': 0,
      'pages written including at least one start transaction ID': 1126,
      'pages written including at least one stop durable timestamp': 0,
      'pages written including at least one stop timestamp': 0,
      'pages written including at least one stop transaction ID': 0,
      'records written including a prepare': 0,
      'records written including a start durable timestamp': 0,
      'records written including a start timestamp': 0,
      'records written including a start transaction ID': 1509,
      'records written including a stop durable timestamp': 0,
      'records written including a stop timestamp': 0,
      'records written including a stop transaction ID': 0
    },
    session: {
      'object compaction': 0,
      'tiered operations dequeued and processed': 0,
      'tiered operations scheduled': 0,
      'tiered storage local retention time (secs)': 0,
      'tiered storage object size': 0
    },
    transaction: {
      'race to read prepared update retry': 0,
      'rollback to stable history store records with stop timestamps older than newer records': 0,
      'rollback to stable inconsistent checkpoint': 0,
      'rollback to stable keys removed': 0,
      'rollback to stable keys restored': 0,
      'rollback to stable restored tombstones from history store': 0,
      'rollback to stable restored updates from history store': 0,
      'rollback to stable skipping delete rle': 0,
      'rollback to stable skipping stable rle': 0,
      'rollback to stable sweeping history store keys': 0,
      'rollback to stable updates removed from history store': 0,
      'transaction checkpoints due to obsolete pages': 0,
      'update conflicts': 0
    }
  },
  nindexes: 1,
  indexBuilds: [],
  totalIndexSize: 81256448,
  totalSize: 158285824,
  indexSizes: { 'ts_-1': 81256448 },
  scaleFactor: 1,
  ok: 1
}