Expiry pager uses stale time

PagingVisitor stores the current time at creation, and while visiting items compares them against that time.

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bool isExpired = (currentBucket->getState() == vbucket_state_active) &&

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                     v.isExpired(startTime) && !v.isDeleted();

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PagingVisitor::PagingVisitor(...) :

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...

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      startTime(ep_real_time()),

Anecdotally, for large (~200GB) buckets with an expiry-heavy workload, the paging visitor has been seen to run for 1h30m.

In an ephemeral bucket with low purge intervals, this may mean logically expired items might not be deleted until the current expiry pager run ends and the next begins, delaying memory recovery.

Checking the current time for every item may be more expensive; a good compromise may be to update the cached time before visiting each vbucket.