Version Tokens •In contrast to argument handling for the functions that manipulate the server token list, whitespace surrounding token name arguments is not ignored and  =  and  ;  characters are permitted. •It is possible to lock nonexisting token names. This does not create the tokens. •Timeout values are nonnegative integers representing the time in seconds to wait to acquire locks before timing out with an error. If the timeout is 0, there is no waiting and the function produces an error if locks cannot be acquired immediately. •Version Tokens locking functions are based on the locking service described at Section 5.6.9.1, “The Locking Service” . • version_tokens_session •A token name in the  version_tokens_session  value is not present in the server token list. In this case, an  ER_VTOKEN_PLUGIN_TOKEN_NOT_FOUND  error occurs. •A token value in the  version_tokens_session  value differs from the value of the corresponding token in the server token list. In this case, an  ER_VTOKEN_PLUGIN_TOKEN_MISMATCH  error occurs. 1108 mysql>  SELECT version_tokens_set(’tok1=a;tok2=b;tok3=c’); +--------------------------------------------+ | version_tokens_set(’tok1=a;tok2=b;tok3=c’) | +--------------------------------------------+ | 3 version tokens set. | Version Tokens System Variables Suppose that a management application has set the server token list as follows: It is not a mismatch for the server version token list to include a token not named in the version_tokens_session  value. If the  version_tokens_session  variable has a nonempty value, any mismatch between its value and the server version token list results in an error for any statement the session sends to the server. A mismatch occurs under these conditions: If the  version_tokens_session  variable is  NULL  (the default) or has an empty value, any server version token list matches. (In effect, an empty value disables matching requirements.) The session value of this variable specifies the client version token list and indicates the tokens that the client session requires the server version token list to have. System variables: Version Tokens supports the following system variables. These variables are unavailable unless the Version Tokens plugin is installed (see Section 5.6.6.2, “Installing or Uninstalling Version Tokens” ). Command-Line Format --version-tokens-session=value System Variable version_tokens_session Scope Global, Session Dynamic Yes SET_VAR  Hint Applies No Type String Default Value NULL