Databases Reference
In-Depth Information
Request:
Message Header, Request Payload
MongoDB
Server
Client
Response:
Message Header, Request Payload
FIGURE 13-1
The MongoDB wire protocol allows a number of operations. The allowed operations are as follows:
RESERVED
is also an operation, which was formerly used for
OP_GET_BY_OID
. It's
not listed in the list of opcodes as it's not actively used.
OP_INSERT
(code: 2002) —
Insert a document. The “create” operation in CRUD jargon.
➤
CRUD, which stands for Create, Read, Update and Delete, are standard data
management operations. Many systems and interfaces that interact with
data facilitate the CRUD operations.
OP_UPDATE
(code: 2001) —
Update a document. The update operation in CRUD.
OP_QUERY
(code: 2004) —
Query a collection of documents. The “read” operation in
CRUD.
➤
➤
OP_GET_MORE
(code: 2005)
— Get more data from a query. Query response can contain a
large number of documents. To enhance performance and avoid sending the entire set of
documents, databases involve the concept of a cursor that allows for incremental fetching
of the records. The
OP_GET_MORE
operation facilitates fetching additional documents via a
cursor.
OP_REPLY
(code: 1)
— Reply to a client request. This operation sends responses in reply to
OP_QUERY
and
OP_GET_MORE
operations.
➤
➤
OP_KILL_CURSORS
(code: 2007)
— Operation to close a cursor.
OP_DELETE
(code: 2006)
— Delete a document.
➤
➤
OP_MSG
(code: 1000)
— Generic message command.
Every request and response message has a header. A standard message header has the following
properties:
➤
messageLength
— The length of the message in bytes. Paradoxically, the length includes
4 bytes to hold the length value.
➤
