According to description of permissions_validity_in_ms the permissions_cache is enabled if this
value is set to a non-zero value. Otherwise the permissions_cache is disabled.
According to the permissions_update_interval_in_ms description it must have a non-zero value if permissions_cache
is enabled.
permissions_cache_max_entries description doesn't explicitly state it but it makes no sense to allow it to be zero
if permissions_cache is enabled.
Signed-off-by: Vlad Zolotarov <vladz@scylladb.com>
This patch changes the way a loading_cache works.
Before this patch:
1) If a permissions key is not in the cache it's loaded in the foreground and the original
query is blocked till the permissions are loaded.
2) Every _period the timer does the following:
1) If a value was loaded more than _expiry time ago it is removed from the cache.
2) If the cache is too big - the less recently loaded values are removed till the cache
fits the requested size.
After this patch:
1) If a permissions key is not in the cache it's loaded in the foreground and the original
query is blocked till the permissions are loaded.
2) Every _period the timer does the following:
1) If a value in the cache was loaded or read for the last time more than _expiry time ago - it's removed from the cache.
2) If the cache is too big - the less recently read values are removed till the cache fits the requested size.
3) The values that were loaded more than _refresh time ago are re-read in the background.
The new implementation allows to minimize the amount of the foreground reads for a frequently used value to a single
event (when the value is loaded for the first time).
It also ensures we do not reload values we no longer need.
Signed-off-by: Vlad Zolotarov <vladz@scylladb.com>
