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Control multi-shard modify locks with enable_deadlock_prevention

pull/2494/head
Marco Slot 2018-11-26 14:07:06 +01:00
parent e8f3b32b64
commit aff37cf1bc
4 changed files with 92 additions and 8 deletions
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14
src/backend/distributed/executor/multi_router_executor.c
View File

@ -369,9 +369,21 @@ AcquireExecutorMultiShardLocks(List *taskList)
* In either case, ShareUpdateExclusive has the desired effect, since
* it conflicts with itself and ExclusiveLock (taken by non-commutative
* writes).
*
* However, some users find this too restrictive, so we allow them to
* reduce to a RowExclusiveLock when citus.enable_deadlock_prevention
* is enabled, which lets multi-shard modifications run in parallel as
* long as they all disable the GUC.
*/
lockMode = ShareUpdateExclusiveLock;
if (EnableDeadlockPrevention)
{
lockMode = ShareUpdateExclusiveLock;
}
else
{
lockMode = RowExclusiveLock;
}
}
else
{

14
src/backend/distributed/shared_library_init.c
View File

@ -565,15 +565,17 @@ RegisterCitusConfigVariables(void)
DefineCustomBoolVariable(
"citus.enable_deadlock_prevention",
gettext_noop("Prevents transactions from expanding to multiple nodes"),
gettext_noop("When enabled, consecutive DML statements that write to "
"shards on different nodes are prevented to avoid creating "
"undetectable distributed deadlocks when performed "
"concurrently."),
gettext_noop("Avoids deadlocks by preventing concurrent multi-shard commands"),
gettext_noop("Multi-shard modifications such as UPDATE, DELETE, and "
"INSERT...SELECT are typically executed in parallel. If multiple "
"such commands run concurrently and affect the same rows, then "
"they are likely to deadlock. When enabled, this flag prevents "
"multi-shard modifications from running concurrently when they "
"affect the same shards in order to prevent deadlocks."),
&EnableDeadlockPrevention,
true,
PGC_USERSET,
GUC_NO_SHOW_ALL,
0,
NULL, NULL, NULL);
DefineCustomBoolVariable(

47
src/test/regress/expected/isolation_multi_shard_modify_vs_all.out
View File

@ -62,6 +62,53 @@ step s2-commit:
COMMIT;
starting permutation: s1-begin s1-update_even_concurrently s2-begin s2-update_odd_concurrently s1-commit s2-commit
step s1-begin:
BEGIN;
step s1-update_even_concurrently:
SET citus.enable_deadlock_prevention TO off;
UPDATE users_test_table SET value_1 = 3 WHERE user_id % 2 = 0;
SET citus.enable_deadlock_prevention TO on;
step s2-begin:
BEGIN;
step s2-update_odd_concurrently:
SET citus.enable_deadlock_prevention = off;
UPDATE users_test_table SET value_1 = 3 WHERE user_id % 2 = 1;
SET citus.enable_deadlock_prevention TO on;
step s1-commit:
COMMIT;
step s2-commit:
COMMIT;
starting permutation: s1-begin s1-update_even_concurrently s2-begin s2-update_value_1_of_4_or_6_to_4 s1-commit s2-commit
step s1-begin:
BEGIN;
step s1-update_even_concurrently:
SET citus.enable_deadlock_prevention TO off;
UPDATE users_test_table SET value_1 = 3 WHERE user_id % 2 = 0;
SET citus.enable_deadlock_prevention TO on;
step s2-begin:
BEGIN;
step s2-update_value_1_of_4_or_6_to_4:
UPDATE users_test_table SET value_1 = 4 WHERE user_id = 4 or user_id = 6;
<waiting ...>
step s1-commit:
COMMIT;
step s2-update_value_1_of_4_or_6_to_4: <... completed>
step s2-commit:
COMMIT;
starting permutation: s1-begin s1-update_value_1_of_1_or_3_to_5 s2-begin s2-update_value_1_of_4_or_6_to_4 s1-commit s2-commit s2-select
step s1-begin:
BEGIN;

25
src/test/regress/specs/isolation_multi_shard_modify_vs_all.spec
View File

@ -55,6 +55,13 @@ step "s1-update_all_value_1"
UPDATE users_test_table SET value_1 = 3;
}
step "s1-update_even_concurrently"
{
SET citus.enable_deadlock_prevention TO off;
UPDATE users_test_table SET value_1 = 3 WHERE user_id % 2 = 0;
SET citus.enable_deadlock_prevention TO on;
}
step "s1-update_value_1_of_1_or_3_to_5"
{
UPDATE users_test_table SET value_1 = 5 WHERE user_id = 1 or user_id = 3;
@ -107,6 +114,13 @@ step "s2-update_all_value_1"
UPDATE users_test_table SET value_1 = 6;
}
step "s2-update_odd_concurrently"
{
SET citus.enable_deadlock_prevention = off;
UPDATE users_test_table SET value_1 = 3 WHERE user_id % 2 = 1;
SET citus.enable_deadlock_prevention TO on;
}
step "s2-update_value_1_of_1_or_3_to_8"
{
UPDATE users_test_table SET value_1 = 8 WHERE user_id = 1 or user_id = 3;
@ -125,10 +139,19 @@ step "s2-commit"
# test with parallel connections
permutation "s1-begin" "s1-update_all_value_1" "s2-begin" "s2-select" "s1-commit" "s2-select" "s2-commit"
permutation "s1-begin" "s1-update_all_value_1" "s2-begin" "s2-update_all_value_1" "s1-commit" "s2-commit"
# test without deadlock prevention (first does not conflict, second does)
permutation "s1-begin" "s1-update_even_concurrently" "s2-begin" "s2-update_odd_concurrently" "s1-commit" "s2-commit"
permutation "s1-begin" "s1-update_even_concurrently" "s2-begin" "s2-update_value_1_of_4_or_6_to_4" "s1-commit" "s2-commit"
# test with shard pruning (should not conflict)
permutation "s1-begin" "s1-update_value_1_of_1_or_3_to_5" "s2-begin" "s2-update_value_1_of_4_or_6_to_4" "s1-commit" "s2-commit" "s2-select"
permutation "s1-begin" "s1-update_value_1_of_1_or_3_to_5" "s2-begin" "s2-update_value_1_of_1_or_3_to_8" "s1-commit" "s2-commit" "s2-select"
# test with inserts
permutation "s1-begin" "s1-update_all_value_1" "s2-begin" "s2-insert-to-table" "s1-commit" "s2-commit" "s2-select"
permutation "s1-begin" "s1-update_all_value_1" "s2-begin" "s2-insert-into-select" "s1-commit" "s2-commit" "s2-select"
# multi-shard update affecting the same rows
permutation "s1-begin" "s2-begin" "s1-update_value_1_of_1_or_3_to_5" "s2-update_value_1_of_1_or_3_to_8" "s1-commit" "s2-commit"
# multi-shard update affecting the different rows
@ -143,4 +166,4 @@ permutation "s1-begin" "s1-change_connection_mode_to_sequential" "s1-update_valu
# multi-shard update affecting the same rows
permutation "s1-begin" "s2-begin" "s1-change_connection_mode_to_sequential" "s2-change_connection_mode_to_sequential" "s1-update_value_1_of_1_or_3_to_5" "s2-update_value_1_of_1_or_3_to_8" "s1-commit" "s2-commit"
# multi-shard update affecting the different rows
permutation "s1-begin" "s2-begin" "s1-change_connection_mode_to_sequential" "s2-change_connection_mode_to_sequential" "s2-update_value_1_of_1_or_3_to_8" "s1-update_value_1_of_2_or_4_to_5" "s1-commit" "s2-commit"
permutation "s1-begin" "s2-begin" "s1-change_connection_mode_to_sequential" "s2-change_connection_mode_to_sequential" "s2-update_value_1_of_1_or_3_to_8" "s1-update_value_1_of_2_or_4_to_5" "s1-commit" "s2-commit"