there were two lssues, one is taht BGREWRITEAOF failed since the initial one was still in progress
the solution for this one is to enable appendonly from the server startup so there's no initial aofrw.
the other problem was 0 loading progress events, theory is that on some
platforms a sleep of 1 will cause a much greater delay due to the context
switch, but on other platform it doesn't. in theory a sleep of 100 micro
for 1k keys whould take 100ms, and with hz of 500 we should be gettering
50 events (one every 2ms). in practise it doesn't work like that, so trying
to find a sleep that would be long enough but still not cause the test to take
too long.
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