Ledge Cache Tags notes

cache_tags.txt

Cache Tags

TODO

    housekeeping gracefulness

    housekeeping tests
    case tests
    multi tag tests

    unit tests

Tags
    tag_id = <http_host>:<tagname>

    set of full keys - no ttl

    ledge:cache_tag:<http_host>:<tagname>
        ledge:cache:<key_spec>#<vary_key>::main

    on refresh
        determine tag sets from cached response
        remove from all tag sets

    on save
         always sadd - touches tag key

    Evicted entries might exist in an old tag set, but house keeping should catch that
    and the purge job checks first


    Response header: 'Cache-Tags: tag1, tag2'

Housekeeping
    Set of all tags in system cache_tag sets to keep track - no ttl

    recurring background job to clean up
        - Get list of all tag sets
        - iterate
            - if tag set missing, remove from global set
            - iterate over main keys
                - if main key missing remove from tag set
                - if cached response no logner matches, remove from tag set
        sscan sets?
        sleep for gracefulness?


Purge cache tag
    - Look up tag set
    - iterate
        - headless purge -- see wildcard purge job
            - remove from tag set IF cached response matches current tag set


purge delete     - removes from all tag set
purge invalidate - retain for revalidation
purge revalidate - retain for revalidation