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To start with let us see the impact of work done to improve the performance of hash indexes. Below is the performance data of the pgbench read-only workload to compare the performance difference of Hash indexes between 9.6 and HEAD on IBM POWER-8 having 24 cores, 192 hardware threads, 492GB RAM.

The workload is such that all the data fits in shared buffers (scale factor is 300 (~4.5GB) and shared_buffers is 8GB).

And chart itself says it is a median of 3 5 minute runs.