Piotr Grabowski 3f2224a47f loading_cache: force minimum size of unprivileged ...

This patch enforces a minimum size of unprivileged section when
performing shrink() operation.

When the cache is shrank, we still drop entries first from unprivileged
section (as before this commit), however if this section is already small
(smaller than max_size / 2), we will drop entries from the privileged
section.

For example if the cache could store at most 50 entries and there are 49 
entries in privileged section, after adding 5 entries (that would go to 
unprivileged section) 4 of them would get evicted and only the 5th one 
would stay. This caused problems with BATCH statements where all 
prepared statements in the batch have to stay in cache at the same time 
for the batch to correctly execute.

New tests are added to check this behavior and bookkeeping of section
sizes. 

Fixes #10440.

2022-04-29 19:19:04 +02:00

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