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Commit5882ca6

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Call xlc __isync() after, not before, associated compare-and-swap.
Architecture reference material specifies this order, and s_lock.hinline assembly agrees. The former order failed to provide mutualexclusion to lwlock.c and perhaps to other clients. The two xlcbuildfarm members, hornet and mandrill, have failed sixteen times withduplicate key errors involving pg_class_oid_index or pg_type_oid_index.Back-patch to 9.5, where commitb64d92fintroduced atomics.Reviewed by Andres Freund and Tom Lane.
1 parent481725c commit5882ca6

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5 files changed

+47
-8
lines changed

5 files changed

+47
-8
lines changed

‎src/bin/pgbench/.gitignore

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@@ -1,3 +1,4 @@
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/exprparse.c
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/exprscan.c
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/pgbench
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/tmp_check/

‎src/bin/pgbench/Makefile

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@@ -40,3 +40,9 @@ clean distclean:
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maintainer-clean: distclean
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rm -f exprparse.c exprscan.c
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check:
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$(prove_check)
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installcheck:
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$(prove_installcheck)

‎src/bin/pgbench/t/001_pgbench.pl

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@@ -0,0 +1,25 @@
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use strict;
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use warnings;
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use PostgresNode;
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use TestLib;
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use Test::Moretests=> 3;
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# Test concurrent insertion into table with UNIQUE oid column. DDL expects
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# GetNewOidWithIndex() to successfully avoid violating uniqueness for indexes
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# like pg_class_oid_index and pg_proc_oid_index. This indirectly exercises
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# LWLock and spinlock concurrency. This test makes a 5-MiB table.
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my$node = get_new_node('main');
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$node->init;
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$node->start;
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$node->psql('postgres',
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'CREATE UNLOGGED TABLE oid_tbl () WITH OIDS;'
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.'ALTER TABLE oid_tbl ADD UNIQUE (oid);');
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my$script =$node->basedir .'/pgbench_script';
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append_to_file($script,
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'INSERT INTO oid_tbl SELECT FROM generate_series(1,1000);');
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$node->command_like(
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[qw(pgbench --no-vacuum --client=5 --protocol=prepared
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--transactions=25 --file),$script ],
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qr{processed: 125/125},
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'concurrent OID generation');

‎src/include/port/atomics/generic-xlc.h

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@@ -40,19 +40,23 @@ static inline bool
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pg_atomic_compare_exchange_u32_impl(volatilepg_atomic_uint32*ptr,
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uint32*expected,uint32newval)
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{
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/*
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* XXX: __compare_and_swap is defined to take signed parameters, but that
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* shouldn't matter since we don't perform any arithmetic operations.
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*/
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boolret=__compare_and_swap((volatileint*)&ptr->value,
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(int*)expected, (int)newval);
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/*
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* xlc's documentation tells us:
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* "If __compare_and_swap is used as a locking primitive, insert a call to
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* the __isync built-in function at the start of any critical sections."
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*
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* The critical section begins immediately after __compare_and_swap().
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*/
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__isync();
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/*
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* XXX: __compare_and_swap is defined to take signed parameters, but that
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* shouldn't matter since we don't perform any arithmetic operations.
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*/
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return__compare_and_swap((volatileint*)&ptr->value,
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(int*)expected, (int)newval);
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returnret;
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}
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#definePG_HAVE_ATOMIC_FETCH_ADD_U32
@@ -69,10 +73,12 @@ static inline bool
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pg_atomic_compare_exchange_u64_impl(volatilepg_atomic_uint64*ptr,
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uint64*expected,uint64newval)
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{
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boolret=__compare_and_swaplp((volatilelong*)&ptr->value,
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(long*)expected, (long)newval);
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__isync();
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return__compare_and_swaplp((volatilelong*)&ptr->value,
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(long*)expected, (long)newval);;
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returnret;
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}
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#definePG_HAVE_ATOMIC_FETCH_ADD_U64

‎src/tools/msvc/clean.bat

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@@ -94,6 +94,7 @@ if exist src\bin\pg_basebackup\tmp_check rd /s /q src\bin\pg_basebackup\tmp_chec
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ifexist src\bin\pg_config\tmp_checkrd /s /q src\bin\pg_config\tmp_check
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ifexist src\bin\pg_ctl\tmp_checkrd /s /q src\bin\pg_ctl\tmp_check
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ifexist src\bin\pg_rewind\tmp_checkrd /s /q src\bin\pg_rewind\tmp_check
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ifexist src\bin\pgbench\tmp_checkrd /s /q src\bin\pgbench\tmp_check
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ifexist src\bin\scripts\tmp_checkrd /s /q src\bin\scripts\tmp_check
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REM Clean up datafiles built with contrib

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