Re: pg_basebackup misses to report checksum error

On Wed, May 6, 2020 at 5:48 PM Ashwin Agrawal <aagrawal@pivotal.io> wrote:
> If pg_basebackup is not able to read BLCKSZ content from file, then it
> just emits a warning "could not verify checksum in file "____" block
> X: read buffer size X and page size 8192 differ" currently but misses
> to error with "checksum error occurred". Only if it can read 8192 and
> checksum mismatch happens will it error in the end.

I don't think it's a good idea to conflate "hey, we can't checksum
this because the size is strange" with "hey, the checksum didn't
match". Suppose the a file has 1000 full blocks and a partial block.
All 1000 blocks have good checksums. With your change, ISTM that we'd
first emit a warning saying that the checksum couldn't be verified,
and then we'd emit a second warning saying that there was 1 checksum
verification failure, which would also be reported to the stats
system. I don't think that's what we want. There might be an argument
for making this code trigger...

        ereport(ERROR,
                (errcode(ERRCODE_DATA_CORRUPTED),
                 errmsg("checksum verification failure during base backup")));

...but I wouldn't for that reason inflate the number of blocks that
are reported as having failures.

YMMV, of course.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company