On Sat, May 6, 2023 at 9:58 PM Evgeny Morozov <postgresql3@xxxxxxxxxxxxxxxxx> wrote: > Right - I should have realised that! base/1414389/2662 is indeed all > nulls, 32KB of them. I included the file anyway in > https://objective.realityexists.net/temp/pgstuff2.zip OK so it's not just page 0, you have 32KB or 4 pages of all zeroes. That's the expected length of that relation when copied from the initial template, and consistent with the pg_waldump output (it uses FPIs to copy blocks 0-3). We can't see the block contents but we know that block 2 definitely is not all zeroes at that point because there are various modifications to it, which not only write non-zeroes but must surely have required a sane page 0. So it does indeed look like something unknown has replaced 32KB of data with 32KB of zeroes underneath us. Are there more non-empty files that are all-zeroes? Something like this might find them: for F in base/1414389/* do if [ -s $F ] && ! xxd -p $F | grep -qEv '^(00)*$' > /dev/null then echo $F fi done
