On 2020-Sep-03, Tom Lane wrote: > Alvaro Herrera <alvhe...@2ndquadrant.com> writes: > > Well, the intention there is to cast the first operand (which is uint32) > > so that it turns into signed 64-bits; the subtraction then occurs in 64 > > bit arithmetic normally. If I let the subtraction occur in 32-bit width > > unsigned, the result might overflow 32 bits. > > Uh ... is it really possible for gotlen to be more than total_len? > (I've not looked at the surrounding code here, but that seems weird.)
Well, as I understand, total_len comes from one page, and gotlen comes from the continuation record(s) in the next page(s) of WAL. So if things are messed up, it could happen. (This *is* the code that validates the record, so it can't make too many assumptions.) -- Álvaro Herrera https://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
