Merge "Improve help text of image cache opts"
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@ -34,17 +34,133 @@ LOG = logging.getLogger(__name__)
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image_cache_opts = [
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cfg.StrOpt('image_cache_driver', default='sqlite',
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help=_('The driver to use for image cache management.')),
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choices=('sqlite', 'xattr'), ignore_case=True,
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help=_("""
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The driver to use for image cache management.
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This configuration option provides the flexibility to choose between the
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different image-cache drivers available. An image-cache driver is responsible
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for providing the essential functions of image-cache like write images to/read
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images from cache, track age and usage of cached images, provide a list of
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cached images, fetch size of the cache, queue images for caching and clean up
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the cache, etc.
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The essential functions of a driver are defined in the base class
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``glance.image_cache.drivers.base.Driver``. All image-cache drivers (existing
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and prospective) must implement this interface. Currently available drivers
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are ``sqlite`` and ``xattr``. These drivers primarily differ in the way they
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store the information about cached images:
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* The ``sqlite`` driver uses a sqlite database (which sits on every glance
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node locally) to track the usage of cached images.
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* The ``xattr`` driver uses the extended attributes of files to store this
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information. It also requires a filesystem that sets ``atime`` on the files
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when accessed.
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Services which consume this:
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* glance-api
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Possible values:
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* sqlite
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* xattr
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Related options:
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* None
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""")),
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cfg.IntOpt('image_cache_max_size', default=10 * units.Gi, # 10 GB
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help=_('The upper limit (the maximum size of accumulated '
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'cache in bytes) beyond which the cache pruner, if '
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'running, starts cleaning the image cache.')),
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min=0,
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help=_("""
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The upper limit on cache size, in bytes, after which the cache-pruner cleans
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up the image cache.
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NOTE: This is just a threshold for cache-pruner to act upon. It is NOT a
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hard limit beyond which the image cache would never grow. In fact, depending
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on how often the cache-pruner runs and how quickly the cache fills, the image
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cache can far exceed the size specified here very easily. Hence, care must be
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taken to appropriately schedule the cache-pruner and in setting this limit.
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Glance caches an image when it is downloaded. Consequently, the size of the
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image cache grows over time as the number of downloads increases. To keep the
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cache size from becoming unmanageable, it is recommended to run the
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cache-pruner as a periodic task. When the cache pruner is kicked off, it
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compares the current size of image cache and triggers a cleanup if the image
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cache grew beyond the size specified here. After the cleanup, the size of
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cache is less than or equal to size specified here.
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Services which consume this:
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* None (consumed by cache-pruner, an independent periodic task)
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Possible values:
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* Any non-negative integer
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Related options:
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* None
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""")),
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cfg.IntOpt('image_cache_stall_time', default=86400, # 24 hours
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help=_('The amount of time to let an incomplete image remain '
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'in the cache, before the cache cleaner, if running, '
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'will remove the incomplete image.')),
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min=0,
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help=_("""
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The amount of time, in seconds, an incomplete image remains in the cache.
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Incomplete images are images for which download is in progress. Please see the
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description of configuration option ``image_cache_dir`` for more detail.
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Sometimes, due to various reasons, it is possible the download may hang and
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the incompletely downloaded image remains in the ``incomplete`` directory.
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This configuration option sets a time limit on how long the incomplete images
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should remain in the ``incomplete`` directory before they are cleaned up.
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Once an incomplete image spends more time than is specified here, it'll be
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removed by cache-cleaner on its next run.
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It is recommended to run cache-cleaner as a periodic task on the Glance API
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nodes to keep the incomplete images from occupying disk space.
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Services which consume this:
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* None (consumed by cache-cleaner, an independent periodic task)
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Possible values:
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* Any non-negative integer
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Related options:
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* None
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""")),
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cfg.StrOpt('image_cache_dir',
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help=_('Base directory that the image cache uses.')),
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help=_("""
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Base directory for image cache.
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This is the location where image data is cached and served out of. All cached
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images are stored directly under this directory. This directory also contains
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three subdirectories, namely, ``incomplete``, ``invalid`` and ``queue``.
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The ``incomplete`` subdirectory is the staging area for downloading images. An
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image is first downloaded to this directory. When the image download is
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successful it is moved to the base directory. However, if the download fails,
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the partially downloaded image file is moved to the ``invalid`` subdirectory.
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The ``queue``subdirectory is used for queuing images for download. This is
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used primarily by the cache-prefetcher, which can be scheduled as a periodic
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task like cache-pruner and cache-cleaner, to cache images ahead of their usage.
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Upon receiving the request to cache an image, Glance touches a file in the
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``queue`` directory with the image id as the file name. The cache-prefetcher,
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when running, polls for the files in ``queue`` directory and starts
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downloading them in the order they were created. When the download is
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successful, the zero-sized file is deleted from the ``queue`` directory.
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If the download fails, the zero-sized file remains and it'll be retried the
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next time cache-prefetcher runs.
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Services which consume this:
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* glance-api
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Possible values:
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* A valid path
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Related options:
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* ``image_cache_sqlite_db``
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""")),
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]
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CONF = cfg.CONF
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@ -38,8 +38,26 @@ LOG = logging.getLogger(__name__)
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sqlite_opts = [
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cfg.StrOpt('image_cache_sqlite_db', default='cache.db',
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help=_('The path to the sqlite file database that will be '
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'used for image cache management.')),
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help=_("""
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The relative path to sqlite file database that will be used for image cache
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management.
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This is a relative path to the sqlite file database that tracks the age and
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usage statistics of image cache. The path is relative to image cache base
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directory, specified by the configuration option ``image_cache_dir``.
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This is a lightweight database with just one table.
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Services which consume this:
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* glance-api
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Possible values:
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* A valid relative path to sqlite file database
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Related options:
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* ``image_cache_dir``
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""")),
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]
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CONF = cfg.CONF
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