Console log showing how to reproduce the mongodb oplog size bug

mongo bug log

[george@c7 ~]$ docker run --name mongo-server -d mongo:4.2.5 mongod --replSet rs0
f6810e93af750a6d4520d9d708233b52ca5f5ace07d8aa6505e69a81fafbba56

[george@c7 ~]$ docker cp mongo-bug/ f6810e93af75:/mongo-bug

[george@c7 ~]$ docker exec -it f6810e93af75 bash

root@f6810e93af75:/# ls mongo-bug/
go.mod  go.sum  init  largetx

root@f6810e93af75:/# echo "rs.initiate()" | mongo
MongoDB shell version v4.2.5
connecting to: mongodb://127.0.0.1:27017/?compressors=disabled&gssapiServiceName=mongodb
Implicit session: session { "id" : UUID("a6ae214c-7e7c-4cdb-94f0-5e678c52e822") }
MongoDB server version: 4.2.5
{
        "info2" : "no configuration specified. Using a default configuration for the set",
        "me" : "f6810e93af75:27017",
        "ok" : 1,
        "$clusterTime" : {
                "clusterTime" : Timestamp(1586351017, 1),
                "signature" : {
                        "hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
                        "keyId" : NumberLong(0)
                }
        },
        "operationTime" : Timestamp(1586351017, 1)
}
bye

root@f6810e93af75:/# /mongo-bug/init/init
2020/04/08 13:03:54 Connecting to mongo...
2020/04/08 13:03:54 Connected, starting session...

root@f6810e93af75:/# /mongo-bug/largetx/largetx & mongodump --oplog
[1] 116
2020-04-08T13:05:26.857+0000    writing admin.system.version to
2020-04-08T13:05:26.859+0000    done dumping admin.system.version (1 document)
2020-04-08T13:05:26.865+0000    writing foo.junk to
2020-04-08T13:05:29.810+0000    done dumping foo.junk (1000005 documents)
2020-04-08T13:05:29.869+0000    writing captured oplog to
2020-04-08T13:05:30.159+0000            dumped 7 oplog entries
[1]+  Done                    /mongo-bug/largetx/largetx

root@f6810e93af75:/# ls -lh dump/
total 81M
drwxr-xr-x 2 root root 4.0K Apr  8 13:05 admin
drwxr-xr-x 2 root root 4.0K Apr  8 13:05 foo
-rw-r--r-- 1 root root  81M Apr  8 13:05 oplog.bson

root@f6810e93af75:/# bsondump dump/oplog.bson
{"ts":{"$timestamp":{"t":1586351109,"i":3}},"t":{"$numberLong":"1"},"h":{"$numberLong":"0"},"v":{"$numberInt":"2"},"op":"c","ns":"config.$cmd","ui":{"$binary":{"base64":"zJUkdrwhSAKm0SbCRajOEA==","subType":"04"}},"wall":{"$date":{"$numberLong":"1586351109590"}},"o":{"createIndexes":"system.sessions","v":{"$numberInt":"2"},"key":{"lastUse":{"$numberInt":"1"}},"name":"lsidTTLIndex","expireAfterSeconds":{"$numberInt":"1800"}}}
{"ts":{"$timestamp":{"t":1586351127,"i":1}},"t":{"$numberLong":"1"},"h":{"$numberLong":"0"},"v":{"$numberInt":"2"},"op":"n","ns":"","wall":{"$date":{"$numberLong":"1586351127763"}},"o":{"msg":"periodic noop"}}
2020-04-08T13:05:40.841+0000    2 objects found
2020-04-08T13:05:40.841+0000    invalid BSONSize: 16777499 bytes

root@f6810e93af75:/# echo "db.dropDatabase()" | mongo foo
MongoDB shell version v4.2.5
connecting to: mongodb://127.0.0.1:27017/foo?compressors=disabled&gssapiServiceName=mongodb
Implicit session: session { "id" : UUID("31e5d8ad-45df-407f-83c6-caaaf3895041") }
MongoDB server version: 4.2.5
{
        "dropped" : "foo",
        "ok" : 1,
        "$clusterTime" : {
                "clusterTime" : Timestamp(1586352438, 1),
                "signature" : {
                        "hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
                        "keyId" : NumberLong(0)
                }
        },
        "operationTime" : Timestamp(1586352438, 1)
}
bye

root@f6810e93af75:/# mongorestore --oplogReplay
2020-04-08T13:15:13.749+0000    using default 'dump' directory
2020-04-08T13:15:13.749+0000    preparing collections to restore from
2020-04-08T13:15:13.751+0000    reading metadata for foo.junk from dump/foo/junk.metadata.json
2020-04-08T13:15:13.762+0000    restoring foo.junk from dump/foo/junk.bson
2020-04-08T13:15:16.748+0000    [........................]  foo.junk  4.55MB/131MB  (3.5%)
2020-04-08T13:15:19.748+0000    [#.......................]  foo.junk  8.74MB/131MB  (6.7%)
2020-04-08T13:15:22.749+0000    [##......................]  foo.junk  13.0MB/131MB  (10.0%)
2020-04-08T13:15:25.751+0000    [###.....................]  foo.junk  17.6MB/131MB  (13.5%)
2020-04-08T13:15:28.752+0000    [####....................]  foo.junk  22.1MB/131MB  (16.9%)
2020-04-08T13:15:31.748+0000    [####....................]  foo.junk  26.5MB/131MB  (20.3%)
2020-04-08T13:15:34.748+0000    [#####...................]  foo.junk  31.3MB/131MB  (24.0%)
2020-04-08T13:15:37.748+0000    [######..................]  foo.junk  36.1MB/131MB  (27.7%)
2020-04-08T13:15:40.753+0000    [#######.................]  foo.junk  40.7MB/131MB  (31.2%)
2020-04-08T13:15:43.748+0000    [########................]  foo.junk  45.4MB/131MB  (34.8%)
2020-04-08T13:15:46.748+0000    [#########...............]  foo.junk  49.7MB/131MB  (38.1%)
2020-04-08T13:15:48.489+0000    [########################]  foo.junk  131MB/131MB  (100.0%)
2020-04-08T13:15:48.489+0000    no indexes to restore
2020-04-08T13:15:48.489+0000    finished restoring foo.junk (1000001 documents, 0 failures)
2020-04-08T13:15:48.489+0000    replaying oplog
2020-04-08T13:15:48.496+0000    applied 1 oplog entries
2020-04-08T13:15:48.496+0000    Failed: restore error: error reading oplog bson input: invalid BSONSize: 16777499 bytes
2020-04-08T13:15:48.496+0000    1000001 document(s) restored successfully. 0 document(s) failed to restore.

root@f6810e93af75:/# mongodump --db local --collection oplog.rs --out oplogdump
2020-04-08T13:24:05.094+0000    writing local.oplog.rs to
2020-04-08T13:24:08.083+0000    local.oplog.rs  716842
2020-04-08T13:24:11.086+0000    local.oplog.rs  1384772
2020-04-08T13:24:13.312+0000    local.oplog.rs  2000135
2020-04-08T13:24:13.312+0000    done dumping local.oplog.rs (2000135 documents)

root@f6810e93af75:/# bsondump oplogdump/local/oplog.rs.bson >/dev/null
2020-04-08T13:25:36.175+0000    1000017 objects found
2020-04-08T13:25:36.176+0000    invalid BSONSize: 16777499 bytes