> On Jun 8, 2022, at 5:45 AM, Bruce Momjian <br...@momjian.us> wrote:
>
> Is this something anyone has even needed or had requested?
I might have put this in amcheck's verify_heapam() had there been an interface
for it. I vaguely recall wanting something like this, yes.
As it stands, verify_heapam() may trigger mdread()'s "could not open file" or
"could not read block" error, in the course of verifying the table. There
isn't an option in amcheck to just verify that the underlying files exist. If
struct f_smgr had a function for validating that all segment files exist, I may
have added an option to amcheck (and the pg_amcheck frontend tool) to quickly
look for missing files.
Looking at smgr/md.c, it seems mdnblocks() is close to what we want, but it
skips already opened segments "to avoid redundant seeks". Perhaps we'd want to
add a function to f_smgr, say "smgr_allexist", to check for all segment files?
I'm not sure how heavy-handed the corresponding mdallexist() function should
be. Should it close all open segments, then reopen and check the size of all
of them by calling mdnblocks()? That seems safer than merely asking the
filesystem if the file exists without verifying that it can be opened.
If we made these changes, and added corresponding quick check options to
amcheck and pg_amcheck, would that meet your current needs? The downside to
using amcheck for this sort of thing is that we did not (and likely will not)
back port it. I have had several occasions to want this functionality
recently, but the customers were on pre-v14 servers, so these tools were not
available anyway.
—
Mark Dilger
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
