The TAP tests whose ok() calls are changed in this commit were relying
on perl operators, rather than equivalents available in Test::More. For
example, rather than the following:
ok($data =~ qr/expr/m, "expr matching");
ok($data !~ qr/expr/m, "expr not matching");
The new test code uses this equivalent:
like($data, qr/expr/m, "expr matching");
unlike($data, qr/expr/m, "expr not matching");
A huge benefit of the new formulation is that it is possible to know
about the values we are checking if a failure happens, making debugging
easier, should the test runs happen in the buildfarm, in the CI or
locally.
This change leads to more test code overall as perltidy likes to make
the code pretty the way it is in this commit.
Author: Sadhuprasad Patro <b.sadhu@gmail.com>
Discussion: https://postgr.es/m/CAFF0-CHhwNx_Cv2uy7tKjODUbeOgPrJpW4Rpf1jqB16_1bU2sg@mail.gmail.com
e85662df44 implemented GetStrictOldestNonRemovableTransactionId() function
for computation of xid horizon that avoid reporting of false errors.
However, GetStrictOldestNonRemovableTransactionId() uses
GetRunningTransactionData() even on standby leading to an assertion failure.
Given that we decided to ignore KnownAssignedXids and standby can't have
own running xids, we switch to use TransamVariables->nextXid as a xid horizon.
Also, revise the comment regarding ignoring KnownAssignedXids with more
detailed reasoning provided by Heikki.
Reported-by: Heikki Linnakangas
Discussion: https://postgr.es/m/42218c4f-2c8d-40a3-8743-4d34dd0e4cce%40iki.fi
Reviewed-by: Heikki Linnakangas
Currently, pg_visibility computes its xid horizon using the
GetOldestNonRemovableTransactionId(). The problem is that this horizon can
sometimes go backward. That can lead to reporting false errors.
In order to fix that, this commit implements a new function
GetStrictOldestNonRemovableTransactionId(). This function computes the xid
horizon, which would be guaranteed to be newer or equal to any xid horizon
computed before.
We have to do the following to achieve this.
1. Ignore processes xmin's, because they consider connection to other databases
that were ignored before.
2. Ignore KnownAssignedXids, because they are not database-aware. At the same
time, the primary could compute its horizons database-aware.
3. Ignore walsender xmin, because it could go backward if some replication
connections don't use replication slots.
As a result, we're using only currently running xids to compute the horizon.
Surely these would significantly sacrifice accuracy. But we have to do so to
avoid reporting false errors.
Inspired by earlier patch by Daniel Shelepanov and the following discussion
with Robert Haas and Tom Lane.
Discussion: https://postgr.es/m/1649062270.289865713%40f403.i.mail.ru
Reviewed-by: Alexander Lakhin, Dmitry Koval
