Currently there is a race condition that occurs between the
dbjobqueue enqueue and dequeue functions. Both queries make
use of the postgres `now()` timestamp function which returns
the timestamp of when the transaction started and not when
the statement is executed. The result of this is a timestamp
for a job's `started_at` field to be earlier than its
`queued_at` field causing a constraint violation.
Since the dequeue query will never be executed before the
enqueue query, changing the postgres timestamp function to
`statement_timestamp()` resolves this issue.
errors.As is meant to check whether err (or other error in its chain) can
be assigned to the value that target is pointing at.
Let's consider this example:
errors.As(err, &pgx.ErrNoRows)
pgx.ErrNoRows (and pgx.ErrTxClosed) is typed as error, thus in all
errors.As calls, the target is typed as *error. Err is always an error.
So this call is basically asking whether error can be assigned to error.
If err != nil, this is always true, thus this check doesn't make any sense
over a plain err != nil.
Go 1.19 now checks this issue and if it's found, it refuses to compile the
code, see:
https://go-review.googlesource.com/c/tools/+/339889
This commit changes usages of errors.As() to errors.Is(). The Is() method
doesn't check assignability but equality (the only different between Is()
and a plain old == operator is that Is() also inspects the whole error chain).
This fixes the check because now, we are basically checking if err (or
any other error in its chain) == pgx.ErrTxClosed which is exactly what we
want.
Signed-off-by: Ondřej Budai <ondrej@budai.cz>
