Heikki Linnakangas was doing some benchmarking last week and discovered something surprising: in some circumstances, unlogged tables were actually slower than permanent tables. Upon examination, he discovered that the problem was caused by CLOG contention, due to hint bits not being set soon enough. This leads to a few questions:
1. What is CLOG?
2. What are hint bits?
3. How does setting hint bits prevent CLOG contention?
4. Why weren't hint bits being set sooner?
Let's take those in order.
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1. What is CLOG?
2. What are hint bits?
3. How does setting hint bits prevent CLOG contention?
4. Why weren't hint bits being set sooner?
Let's take those in order.
Read more »
