Skip to content

Latest commit

 

History

History
62 lines (51 loc) · 3.22 KB

oso_snapshot.md

File metadata and controls

62 lines (51 loc) · 3.22 KB
Raw

OSO Snapshot (opcode 0x65)

Sent by the producer to tell the consumer that a Out of Sequence Order snapshot is to be transmitted or has now been completed.

A snapshot is simply a series of commands that is guaranteed to contain a unique set of keys. An OSO snapshot is exactly this, but differs from a normal DCP snapshot (opcode 0x56) in that it transmits the keys in an undefined order.

The OSO snapshot message contains a flags bit-field which has the following defined flags:

  • 0x01: start This is the start of an OSO snapshot
  • 0x02: end This is the end of an OSO snapshot

An OSO snapshot will only be transmitted if the client has enabled the feature using DCP control enable_out_of_order_snapshots. A correctly written client that makes use of the OSO snapshot should apply the following rules.

  • During in the receipt (after the start and before the end) the client must track the greatest sequence number received (X) in addition to the greatest sequence number received before the start (Y).
  • If the stream fails before receipt of the end, the client must resume from the sequence number Y.
  • If the stream fails after the receipt of the end, the client can resume from sequence number X. ** resuming from sequence number X before the end of an OSO snapshot will result in the client receiving a partial/incorrect view of the vbucket.

The request:

  • Must have extras
  • Must not have key

Encoding Examples

The following example shows the breakdown of the message:

  Byte/     0       |       1       |       2       |       3       |
     /              |               |               |               |
    |0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
    +---------------+---------------+---------------+---------------+
   0| 0x80          | 0x65          | 0x00          | 0x00          |
    +---------------+---------------+---------------+---------------+
   4| 0x04          | 0x00          | 0x00          | 0x00          |
    +---------------+---------------+---------------+---------------+
   8| 0x00          | 0x00          | 0x00          | 0x00          |
    +---------------+---------------+---------------+---------------+
  12| 0xde          | 0xad          | 0xbe          | 0xef          |
    +---------------+---------------+---------------+---------------+
  16| 0x00          | 0x00          | 0x00          | 0x00          |
    +---------------+---------------+---------------+---------------+
  20| 0x00          | 0x00          | 0x00          | 0x00          |
    +---------------+---------------+---------------+---------------+
  24| 0x00          | 0x00          | 0x00          | 0x01          |
    +---------------+---------------+---------------+---------------+

DCP_OSO_SNAPSHOT command
Field           (offset) (value)
Magic           (0)    : 0x80
Opcode          (1)    : 0x65
Key length      (2,3)  : 0x0000
Extra length    (4)    : 0x4
Data type       (5)    : 0x00
Vbucket         (6,7)  : 0x0000
Total body      (8-11) : 0x00000004
Opaque          (12-15): 0xdeadbeef
CAS             (16-23): 0x0000000000000000
  Flags         (24-27): 0x00000001 (start of a snapshot)