GAMBAS BOOK 3.19.1

Many will ask themselves: What is Memcached? On the website https://memcached.org you will find a good answer:

• Memcached is a “…free and open source, high performance distributed memory object caching system.
• It is generic, but intended for use in accelerating dynamic web applications by reducing database load.
• Memcached is an in-memory key-value store for small pieces of arbitrary data (strings, objects) from database call results, API calls or page rendering. Memcached is simple yet powerful”.

The gb.memcached component with its single Memcached class aims to provide you with a fully usable memory interface.

The Memcached class has these properties

Table 22.10.0.1.1 : Properties of the Memcached class

This allows you to create a new Memcached client object, then set selected properties and finally start the configured client:

    Dim hMCClient As Memcached
 
    hMCClient = New Memcached 	        '-- A new MC client(!) is created
    hMCClient.Host = "localhost"      	'-- Default-Host: localhost; Alternative: "127.0.0.1"
    hMCClient.Port = 11211            	'-- Default-Port-Number
    hMCClient.Debug = True            	'-- True → Only for tests in the IDE
 
    If Not hMCClient.Open() Then
       Message.Error(("Memcached.Open-Error") & gb.NewLine & Error.Text & gb.NewLine & Error.Where)
       Return
    Endif

Notes:

• If the Memcached property Debug is set to True, a Memcached client issues all commands sent to the MC server in a console.
• The Memcached status can alternatively assume the following values: Net.Inactive (0) → The connection from the MC client to the MC server is closed. Net.Connected (7) → The MC client is connected to the MC server.
• The default port number for the Memcached server is 11211.

The Memcached class has these five methods:

Table 22.10.0.2.1 : Methods of the Memcached class

The following constants relate to the output of the Memcached.Exec(…) method, among other things!

Table 22.10.0.3.1 : Constants of the Memcached class

You can use the Memcached class like a read-only array Memcached[ ]:

  Dim hMemcached As Memcached
  Dim hMemcachedKey As _Memcached_Key
  hMemcachedKey = hMemcached [ sKey As String ]

A virtual Memcached key object linked to the key 'sKey' (data type String) is returned. This is the preferred method for read and write data access.

The _Memcached_Key class has these two properties:

Table 22.10.0.4.1 : Properties of the _Memcached_Key class

If you save a new key-value pair that does not yet exist on the MC server, for example, hMCClient[sCurKey].CasID returns the value 0.

The _Memcached_Key class has these five methods:

Table 22.10.0.4.2 : Methods of the _Memcached_Key class

Notes:

• The smallest function value of the Decrement ( [ iStep As Integer ] ) method is 0. All further calls to the function then also return 0.
• The iExpire parameter of the Touch method ( iExpire As Integer ) defines the expiry time of the data in seconds. The default value is 0 and means: The value never expires. Regardless of this, the value can be deleted from the cache at any time to make room for other key-value pairs!

You should know this before using the gb.memcached component in practice:

• There is no access control: any MC client connected to an MC server can read all stored data on the MC server and can also write data.
• All data is only stored in the memory. When a programme that uses the gb.memcached component is terminated, the data is no longer available.
• You can only access the data with a unique key. Iterating is not possible!
• Data can be saved either permanently or for a limited time during the runtime of the memcached client. In the latter case, the Memcached server automatically deletes the data.
• The data type for a key is string.
• The data type for a value is either Variant or Object.