Using Cache Pools and Directives
You can use the Command-Line Interface (CLI) to create, modify, and list Cache
Pools and Cache Directives via the hdfs cacheadmin subcommand.
Cache Directives are identified by a unique, non-repeating, 64-bit integer ID. IDs will not be reused even if a Cache Directive is removed.
Cache Pools are identified by a unique string name.
You must first create a Cache Pool, and then add Cache Directives to the Cache Pool.
Cache Pool Commands
addPool-- Adds a new Cache Pool.Usage:
hdfs cacheadmin -addPool <name> [-owner <owner>] [-group <group>] [-mode <mode>] [-limit <limit>] [-maxTtl <maxTtl>]
Options:
Table 3.1. Cache Pool Add Options
Option Description <nameThe name of the pool. <ownerThe user name of the owner of the pool. Defaults to the current user. <groupThe group that the pool is assigned to. Defaults to the primary group name of the current user. <modeThe UNIX-style permissions assigned to the pool. Permissions are specified in octal (e.g. 0755). Pool permissions are set to 0755 by default. <limitThe maximum number of bytes that can be cached by directives in the pool, in aggregate. By default, no limit is set. <maxTtlThe maximum allowed time-to-live for directives being added to the pool. This can be specified in seconds, minutes, hours, and days (e.g. 120s, 30m, 4h, 2d). Valid units are [smhd]. By default, no maximum is set. A value of "never" specifies that there is no limit.
modifyPool-- Modifies the metadata of an existing Cache Pool.Usage:
hdfs cacheadmin -modifyPool <name> [-owner <owner>] [-group <group>] [-mode <mode>] [-limit <limit>] [-maxTtl <maxTtl>]
Options:
Table 3.2. Cache Pool Modify Options
Option Description nameThe name of the pool to modify. ownerThe user name of the owner of the pool. groupThe group that the pool is assigned to. modeThe UNIX-style permissions assigned to the pool. Permissions are specified in octal (e.g. 0755). limitThe maximum number of bytes that can be cached by directives in the pool, in aggregate. maxTtlThe maximum allowed time-to-live for directives being added to the pool. This can be specified in seconds, minutes, hours, and days (e.g. 120s, 30m, 4h, 2d). Valid units are [smdh]. By default, no maximum is set. A value of "never" specifies that there is no limit.
removePool-- Removes a Cache Pool. This command also "un-caches" paths that are associated with the pool.Usage:
hdfs cacheadmin -removePool <name>
Options:
listPools-- Displays information about one or more Cache Pools, such as name, owner, group, permissions, and so on.Usage:
hdfs cacheadmin -listPools [-stats] [<name>]
Options:
Table 3.4. Cache Pools List Options
Option Description statsDisplays additional Cache Pool statistics. nameIf specified, lists only the named Cache Pool.
help-- Displays detailed information about a command.Usage:
hdfs cacheadmin -help <command-name>
Options:
Table 3.5. Cache Pool Help Options
Option Description <command-nameDisplays detailed information for the specified command name. If no command name is specified, detailed help is displayed for all commands.
Cache Directive Commands
addDirective-- Adds a new Cache Directive.Usage:
hdfs cacheadmin -addDirective -path <path> -pool <pool-name> [-force] [-replication <replication>] [-ttl <time-to-live>]
Options:
Table 3.6. Cache Pool Add Directive Options
Option Description <path>The path to the cache directory or file. <pool-name>The Cache Pool to which the Cache Directive will be added. You must have Write permission for the Cache Pool in order to add new directives. <-force>Skips checking of the Cache Pool resource limits. <-replication>The UNIX-style permissions assigned to the pool. Permissions are specified in octal (e.g. 0755). Pool permissions are set to 0755 by default. <limit>The cache replication factor to use. Default setting is 1. <time-to-live>How long the directive is valid. This can be specified in minutes, hours and days (e.g. 30m, 4h, 2d). Valid units are [smdh]. A value of "never" indicates a directive that never expires. If unspecified, the directive never expires.
removeDirective-- Removes a Cache Directive.Usage:
hdfs cacheadmin -removeDirective <id>
Options:
Table 3.7. Cache Pools Remove Directive Options
Option Description <id>The ID of the Cache Directive to remove. You must have Write permission for the pool that the directive belongs to in order to remove it. You can use the -listDirectivescommand to display a list of Cache Directive IDs.
removeDirectives-- Removes all of the Cache Directives in a specified path.Usage:
hdfs cacheadmin -removeDirectives <path>
Options:
Table 3.8. Cache Pool Remove Directives Options
Option Description <path>The path of the Cache Directives to remove. You must have Write permission for the pool that the directives belong to in order to remove them. You can use the -listDirectivescommand to display a list of Cache Directives.
listDirectives-- Returns a list of Cache Directives.Usage:
hdfs cacheadmin -listDirectives [-stats] [-path <path>] [-pool <pool>]
Options:
Table 3.9. Cache Pools List Directives Options
Option Description <path>Lists only the Cache Directives in the specified path. If there is a Cache Directive in the <path> that belongs to a Cache Pool for which you do not have Read access, it will not be listed. <pool>Lists on the Cache Directives in the specified Cache Pool. <-stats>Lists path-based Cache Directive statistics.