Hello, The bug can be reproduced on a standard TPC-H database with scale factor 1. A query returns NULL after query logging is enabled. The computer we use has Intel i7-8700K (12 cores) and 32GB RAM. Please see the details below.

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mclient -d tpch1 -t performance Welcome to mclient, the MonetDB/SQL interactive terminal (Nov2019-SP1) Database: MonetDB v11.35.9 (Nov2019-SP1), 'mapi:monetdb://tigger:50000/tpch1' FOLLOW US on https://twitter.com/MonetDB or https://github.com/MonetDB/MonetDB Type \q to quit, \? for a list of available commands auto commit mode: on sql>select sum(l_extendedprice) from lineitem; +------------------------------------------+ | L2 | +==========================================+ | 229577310901.20 | +------------------------------------------+ 1 tuple sql:0.083 opt:1.056 run:5.898 clk:7.763 ms sql>call sys.querylog_enable(); sql>select sum(l_extendedprice) from lineitem; +------------------------------------------+ | L2 | +==========================================+ | null | +------------------------------------------+ 1 tuple sql:0.095 opt:1.312 run:15.920 clk:25.033 ms

Hanfeng Chen