postgresql/src/backend/utils
Tom Lane b9654cecea Fix ruleutils issues with dropped cols in functions-returning-composite.
Due to lack of concern for the case in the dependency code, it's
possible to drop a column of a composite type even though stored
queries have references to the dropped column via functions-in-FROM
that return the composite type.  There are "soft" references,
namely FROM-clause aliases for such columns, and "hard" references,
that is actual Vars referring to them.  The right fix for hard
references is to add dependencies preventing the drop; something
we've known for many years and not done (and this commit still doesn't
address it).  A "soft" reference shouldn't prevent a drop though.
We've been around on this before (cf. 9b35ddce9, 2c4debbd0), but
nobody had noticed that the current behavior can result in dump/reload
failures, because ruleutils.c can print more column aliases than the
underlying composite type now has.  So we need to rejigger the
column-alias-handling code to treat such columns as dropped and not
print aliases for them.

Rather than writing new code for this, I used expandRTE() which already
knows how to figure out which function result columns are dropped.
I'd initially thought maybe we could use expandRTE() in all cases, but
that fails for EXPLAIN's purposes, because the planner strips a lot of
RTE infrastructure that expandRTE() needs.  So this patch just uses it
for unplanned function RTEs and otherwise does things the old way.

If there is a hard reference (Var), then removing the column alias
causes us to fail to print the Var, since there's no longer a name
to print.  Failing seems less desirable than printing a made-up
name, so I made it print "?dropped?column?" instead.

Per report from Timo Stolz.  Back-patch to all supported branches.

Discussion: https://postgr.es/m/5c91267e-3b6d-5795-189c-d15a55d61dbb@nullachtvierzehn.de
2022-07-21 13:56:02 -04:00
..
activity Create a distinct wait event for POSIX DSM allocation. 2022-07-14 23:56:28 +12:00
adt Fix ruleutils issues with dropped cols in functions-returning-composite. 2022-07-21 13:56:02 -04:00
cache Fix omissions in support for the "regcollation" type. 2022-07-17 17:43:28 -04:00
error Provide log_status_format(), useful for an emit_log_hook. 2022-07-11 12:29:33 -07:00
fmgr Add construct_array_builtin, deconstruct_array_builtin 2022-07-01 11:23:15 +02:00
hash Update copyright for 2022 2022-01-07 19:04:57 -05:00
init Revert 019_replslot_limit.pl related debugging aids. 2022-07-05 11:01:10 -07:00
mb Update copyright for 2022 2022-01-07 19:04:57 -05:00
misc Tweak detail and hint messages to be consistent with project policy 2022-07-20 09:50:12 +09:00
mmgr Replace many MemSet calls with struct initialization 2022-07-16 08:50:49 +02:00
resowner Remove extraneous blank lines before block-closing braces 2022-04-13 19:16:02 +02:00
sort Invent qsort_interruptible(). 2022-07-12 16:30:36 -04:00
time Fix incorrect logic in HaveRegisteredOrActiveSnapshot(). 2022-04-16 16:04:50 -04:00
.gitignore Rearrange makefile rules for running Gen_fmgrtab.pl. 2018-05-03 17:54:18 -04:00
errcodes.txt Add another SQL/JSON error code 2022-07-18 14:26:43 +02:00
Gen_dummy_probes.pl Update copyright for 2022 2022-01-07 19:04:57 -05:00
Gen_dummy_probes.pl.prolog Update copyright for 2022 2022-01-07 19:04:57 -05:00
Gen_dummy_probes.sed Update copyright for 2022 2022-01-07 19:04:57 -05:00
Gen_fmgrtab.pl Update copyright for 2022 2022-01-07 19:04:57 -05:00
generate-errcodes.pl Add output file argument to generate-errcodes.pl 2022-07-18 12:24:35 -07:00
Makefile Clean up temp file from refactored dtrace rule 2022-07-19 07:31:58 +02:00
postprocess_dtrace.sed Refactor dtrace postprocessing make rules 2022-07-18 12:33:02 -07:00
probes.d Update copyright for 2022 2022-01-07 19:04:57 -05:00
README.Gen_dummy_probes Tweak generation of Gen_dummy_probes.pl 2021-05-11 20:02:02 -04:00

# Generating dummy probes

If Postgres isn't configured with dtrace enabled, we need to generate
dummy probes for the entries in probes.d, that do nothing.

This is accomplished in Unix via the sed script `Gen_dummy_probes.sed`. We
used to use this in MSVC builds using the perl utility `psed`, which mimicked
sed. However, that utility disappeared from Windows perl distributions and so
we converted the sed script to a perl script to be used in MSVC builds.

We still keep the sed script as the authoritative source for generating
these dummy probes because except on Windows perl is not a hard requirement
when building from a tarball.

So, if you need to change the way dummy probes are generated, first change
the sed script, and when it's working generate the perl script. This can
be accomplished by using the perl utility s2p.

s2p is no longer part of the perl core, so it might not be on your system,
but it is available on CPAN and also in many package systems. e.g.
on Fedora it can be installed using `cpan App::s2p` or
`dnf install perl-App-s2p`.

The Makefile contains a recipe for regenerating Gen_dummy_probes.pl, so all
you need to do is once you have s2p installed is `make Gen_dummy_probes.pl`
Note that in a VPATH build this will generate the file in the vpath tree,
not the source tree.