The local Database
On this page
mongod instance has its own
local database, which stores data used in the replication process, and other instance-specific data. The
local database is invisible to replication: collections in the
local database are not replicated.
On startup, each
mongodinstance inserts a document into
startup_logwith diagnostic information about the
mongodinstance itself and host information.
startup_logis a capped collection. This information is primarily useful for diagnostic purposes.
For example, the following is a prototype of a document from the
Documents in the
startup_logcollection contain the following fields:
A UTC ISODate value that reflects when the server started.
A string that reports the
startTimein the system’s local time zone.
An embedded document that reports the
mongodruntime options and their values.
local.system.replsetholds the replica set’s configuration object as its single document. To view the object’s configuration information, issue
mongoshell. You can also query this collection directly.
local.oplog.rsis the capped collection that holds the oplog. You set its size at creation using the
oplogSizeMBsetting. To resize the oplog after replica set initiation, use the Change the Size of the Oplog procedure. For additional information, see the Oplog Size section.
This contains an object used internally by replica sets to track replication status.
On the master:
On each slave:
Retryable Writes against
You cannot perform write operations to collections in the
localdatabase with retryable writes enabled.