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counter.md

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Counter support

Overview

Counter extension provides distributed counters for resource management. Values of counters represent how much a resource is consumed. Multiple clients can acquire/release the resources simultaneously.

Each counter has a non-empty name. The maximum name is up to 65535 bytes. The number of resources available for a counter is represented as a 4 byte unsigned integer; this means a counter can manage up to 4294967295 resources.

  • The counter extension is disabled by default.
  • TCP port used for the counter protocol need to be different from that of the memcache protocol.
  • The namespace of counter objects is different from that of the memcache objects.
  • When a connection is closed, all resources acquired through the connection are released automatically.
  • A counter is created dynamically at the first time the counter is acquired.
  • Counters are not replicated.

Protocol

The counter extension has its own binary protocol.

General format of a packet

 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/ HEADER                                                        /
   /                                                               /
   /                                                               /
   /                                                               /
   +---------------+---------------+---------------+---------------+
 12/ COMMAND-SPECIFIC BODY (as needed)                             /
   +---------------+---------------+---------------+---------------+

Request header

 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| Magic         | Opcode        | Flags         | Reserved      |
   +---------------+---------------+---------------+---------------+
  4| Body length                                                   |
   +---------------+---------------+---------------+---------------+
  8| Opaque                                                        |
   +---------------+---------------+---------------+---------------+
   Total 12 bytes
  • Magic is 0x90.
  • Opcode is defined later.
  • Flags is defined later.
  • Reserved is always zero.
  • Body length is a 4 byte unsigned integer in big-endian.
  • Opaque is an arbitrary 4 byte data.

Response header

 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| Magic         | Opcode        | Status        | Reserved      |
   +---------------+---------------+---------------+---------------+
  4| Body length                                                   |
   +---------------+---------------+---------------+---------------+
  8| Opaque                                                        |
   +---------------+---------------+---------------+---------------+
   Total 12 bytes
  • Magic is 0x91.
  • Opcode and Opaque are copied from the corresponding request.
  • Status is defined later.
  • Reserved is always zero.
  • Body length is a 4 byte unsigned integer in big-endian.

Opcodes

Code Operation
0x00 Noop
0x01 Get
0x02 Acquire
0x03 Release
0x10 Stats
0x11 Dump

Flags

No flags are yet defined.

Response status

Code Status
0x00 No error
0x01 Not found
0x04 Invalid arguments
0x21 Resource not available
0x22 Not acquired
0x81 Unknown command
0x82 Out of memory

Packet specifications

Unless otherwise noted, all integers are represented in big-endian.

Error responses

Errors are signaled by the Status field of the response header. Error messages are accompanied in the message body.

Noop

Noop does nothing and returns a success response.

The request and response of Noop has no body.

Acquire

Acquire acquires some resources associated to a counter. In addition to the counter name, the command has two parameters; one is the number of resources to be acquired, and another is the number of total resources.

Note that, unlike semaphores, counters do not keep the resource capacity; the capacity will be specified by the acquire command. This way, users can change the resource capacity dynamically anytime.

Request body:

 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| Resources                                                     |
   +---------------+---------------+---------------+---------------+
  4| Maximum                                                       |
   +---------------+---------------+---------------+---------------+
  8| Name length                   | (Name data) ...
   +---------------+---------------+
   Total 10 + (Name length) bytes

Successful response body:

 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| Resources                                                     |
   +---------------+---------------+---------------+---------------+
   Total 4 bytes
  • Resources is a 4-byte unsigned integer number. This request will acquire this count of resources. If this is zero, Invalid arguments is returned.
  • Maximum is a 4-byte unsigned integer number. This parameter represents the total number of resources. Maximum must be equal to or greater than Resources, otherwise Invalid arguments is returned.
  • Name length is a 2-byte unsigned integer number. If this is zero, Invalid arguments is returned.

If the named counter does not exist, Acquire creates a new counter, sets its consumption to Resources, and returns the success.

Otherwise, if Consumption + Resources <= Maximum where Consumption is the current consumption of the resource, then this request will augment Consumption by Resources, and return the success. Else, this returns Resource not available error.

Release

Release returns the acquired resources back.

Request body:

 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| Resources                                                     |
   +---------------+---------------+---------------+---------------+
  4| Name length                   |  (Name data) ...
   +---------------+---------------+
   Total 6 + (Name length) bytes

A successful response has no body.

  • Resources is the count of resources to return. It can be zero.
  • Name length is a 2-byte unsigned integer number. If this is zero, Invalid arguments is returned.

If the named counter does not exist, Release returns Not found error. If Resources is greater than the current number of acquired resources, Release returns Not acquired error.

Otherwise, the operation succeeds and the value of the counter is increased by Resources.

Get

Get obtains the current consumption of a counter.

Request body:

 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| Name length                   | (Name data) ...
   +---------------+---------------+
   Total 2 + (Name length) bytes

Success response body:

 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| Consumption                                                   |
   +---------------+---------------+---------------+---------------+
   Total 4 bytes
  • Name length is a 2-byte unsigned integer number. If this is zero, Invalid arguments is returned.

If the named counter does not exist, Get returns Not found error.

Stats

Stats obtains statistics information about counters.

Request body: No body.

Successful response body:

The body consists of a series of name-value pairs.

 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| Name length 1                 | Value length 1                |
   +---------------+---------------+---------------+---------------+
  4| Name1 ... Value1 ...
   +---------------+---------------+---------------+---------------+
  N| Name length 2                 | Value length 2                |
   +---------------+---------------+---------------+---------------+
N+4| Name2 ... Value2 ...
   ...
   Total (Body length) bytes.
  • Name is a name of a statistics item.
  • Value is an ASCII text information.

Dump

Dump dumps all counters.

Request body: No body.

Successful responses:

Dump command returns multiple responses for one request.

Each response contains the name of a counter and the current consumption of the resource. The response also contains the maximum consumption of resources in the interval given in the configuration file.

The end of the series of responses are indicated by the response whose body length is zero.

 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| Current consumption                                           |
   +---------------+---------------+---------------+---------------+
  4| Maximum consumption                                           |
   +---------------+---------------+---------------+---------------+
  8| Name length                   | (Name data) ...
   +---------------+---------------+
   Total 10 + (Name length) bytes

Configurations

Following parameters can be specified in the configuration file:

# If true, the counter extension is enabled. (default: false)
counter.enable = false

# TCP port used for the counter protocol. (default: 11215)
counter.port = 11215

# The maximum number of connections in the counter protocol.
# 0 means unlimited. (default: 0)
counter.max_connections = 0

# The size of the counter hash table. (default: 1000000)
counter.buckets = 1000000

# The interval of measuring the maximum number of resource consumption
# in seconds. (default: 86400)
counter.stats_interval = 86400