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## containers Table Column Constraints 

•You must supply a value for db_schema , db_name , key_columns , value_columns  and unique_idx_name_on_key . Specify 0  for flags , cas_column , and expire_time_column  if they are unused. Failing to do so could cause your setup to fail. 

• key_columns : The maximum limit for a memcached  key is 250 characters, which is enforced by memcached . The mapped key must be a non-Null CHAR  or VARCHAR  type. 

• value_columns : Must be mapped to a CHAR , VARCHAR , or BLOB  column. There is no length restriction and the value can be NULL. 

• cas_column : The cas  value is a 64 bit integer. It must be mapped to a BIGINT  of at least 8 bytes. If you do not use this column, set a value of 0  to indicate that it is unused. 

• expiration_time_column : Must mapped to an INTEGER  of at least 4 bytes. Expiration time is defined as a 32-bit integer for Unix time (the number of seconds since January 1, 1970, as a 32-bit value), or the number of seconds starting from the current time. For the latter, the number of seconds may not exceed 60*60*24*30 (the number of seconds in 30 days). If the number sent by a client is larger, the server considers it to be a real Unix time value rather than an offset from the current time. If you do not use this column, set a value of 0  to indicate that it is unused. 

• flags : Must be mapped to an INTEGER  of at least 32-bits and can be NULL. If you do not use this column, set a value of 0  to indicate that it is unused. 

A pre-check is performed at plugin load time to enforce column constraints. If mismatches are found, the plugin is not loaded. 

## Multiple Value Column Mapping 

•During plugin initialization, when InnoDB memcached  is configured with information defined in the containers  table, each mapped column defined in containers.value_columns  is verified against the mapped InnoDB  table. If multiple InnoDB  table columns are mapped, there is a check to ensure that each column exists and is the right type. 

•At run-time, for memcached  insert operations, if there are more delimited values than the number of mapped columns, only the number of mapped values are taken. For example, if there are six mapped columns, and seven delimited values are provided, only the first six delimited values are taken. The seventh delimited value is ignored. 

•If there are fewer delimited values than mapped columns, unfilled columns are set to NULL. If an unfilled column cannot be set to NULL, insert operations fail. 

•If a table has more columns than mapped values, the extra columns do not affect results. 

## The demo_test Example Table 

The innodb_memcached_config.sql  configuration script creates a demo_test  table in the test database, which can be used to verify InnoDB memcached  plugin installation immediately after setup. 

