Re: Schema variables - new implementation for Postgres 15

I don't understand what 0002 patch does relative to the 0001 patch.
Is 0002 to change the error messages from "schema variables" to "session
variables" , in a separate commit to show that the main patch doesn't change
regression results ? Could you add commit messages ?

I mentioned before that there's a pre-existing use of the phrase "session
variable", which you should change to something else:

origin:doc/src/sgml/ref/set_role.sgml: <command>SET ROLE</command> does not process session variables as specified by
origin:doc/src/sgml/ref/set_role.sgml- the role's <link linkend="sql-alterrole"><command>ALTER ROLE</command></link> settings; this only happens during
origin:doc/src/sgml/ref/set_role.sgml- login.

Maybe "session variable" should be added to the glossary.

The new tests crash if debug_discard_caches=on.

2021-12-20 16:15:44.476 CST postmaster[7478] LOG: server process (PID 7657) was terminated by signal 6: Aborted
2021-12-20 16:15:44.476 CST postmaster[7478] DETAIL: Failed process was running: DISCARD VARIABLES;

TRAP: FailedAssertion("sessionvars", File: "sessionvariable.c", Line: 270, PID: 7657)

#2 0x0000564858a4f1a8 in ExceptionalCondition (conditionName=conditionName(at)entry=0x564858b8626d "sessionvars", errorType=errorType(at)entry=0x564858aa700b "FailedAssertion",
fileName=fileName(at)entry=0x564858b86234 "sessionvariable.c", lineNumber=lineNumber(at)entry=270) at assert.c:69
#3 0x000056485874fec6 in sync_sessionvars_xact_callback (event=<optimized out>, arg=<optimized out>) at sessionvariable.c:270
#4 sync_sessionvars_xact_callback (event=<optimized out>, arg=<optimized out>) at sessionvariable.c:253
#5 0x000056485868030a in CallXactCallbacks (event=XACT_EVENT_PRE_COMMIT) at xact.c:3644
#6 CommitTransaction () at xact.c:2178
#7 0x0000564858681975 in CommitTransactionCommand () at xact.c:3043
#8 0x000056485892b7a9 in finish_xact_command () at postgres.c:2722
#9 0x000056485892dc5b in finish_xact_command () at postgres.c:2720
#10 exec_simple_query () at postgres.c:1240
#11 0x000056485892f70a in PostgresMain () at postgres.c:4498
#12 0x000056485889a479 in BackendRun (port=<optimized out>, port=<optimized out>) at postmaster.c:4594
#13 BackendStartup (port=<optimized out>) at postmaster.c:4322
#14 ServerLoop () at postmaster.c:1802
#15 0x000056485889b47c in PostmasterMain () at postmaster.c:1474
#16 0x00005648585c60c0 in main (argc=5, argv=0x564858e553f0) at main.c:198