Hi, In EXPLAIN (BUFFERS), there are two kinds of cache misses that show up as "reads" when in fact they are not reads at all:
1. Relation extension, which in fact writes a zero-filled block. 2. The RBM_ZERO_* modes, which provoke neither read nor write. Here's a suggested fix. I noticed this because I have some patches in development that hit these cases a bit more and the numbers didn't match my expectation. I suppose someone might want a separate counter for zero-filled buffers (they're still buffer interactions and cache misses) but it seems like it's probably below the kind of thing we're interested in counting (though in passing, I notice recently that some kernels keep some free pages pre-zeroed so they can supply them faster, which is curious). -- Thomas Munro http://www.enterprisedb.com
0001-Don-t-count-zero-filled-buffers-as-read-in-EXPLAIN.patch
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