Push the runtime filter from HashJoin down to SeqScan or AM. #724
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| /* append new runtime filters to target node */ | ||
| SeqScanState *sss = castNode(SeqScanState, attr_filter->target); | ||
| sss->filters = list_concat(sss->filters, scankeys); |
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can we merge filter here on the same attno ?
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- Combining Bloom filters will result in a higher False Positive Rate (FPR) compared to using each of the individual Bloom filters separately, so it is not recommended;
- There is the same problem to combine range filters like combining Bloom filters;
There is only one Bloom filter and one range filter on the same attribute in many cases;
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create table t1(a int, b int) with(parallel_workers=2);
create table rt1(a int, b int) with(parallel_workers=2);
create table rt2(a int, b int);
create table rt3(a int, b int);
insert into t1 select i, i from generate_series(1, 100000) i;
insert into t1 select i, i+1 from generate_series(1, 10) i;
insert into rt1 select i, i+1 from generate_series(1, 10) i;
insert into rt2 select i, i+1 from generate_series(1, 10000) i;
insert into rt3 select i, i+1 from generate_series(1, 10) i;
analyze t1;
analyze rt1;
analyze rt2;
analyze rt3;
explain analyze select * from rt1 join t1 on rt1.a = t1.b join rt3 on rt3.a = t1.b;
postgres=# explain select * from rt1 join t1 on rt1.a = t1.b join rt3 on rt3.a = t1.b;
QUERY PLAN
--------------------------------------------------------------------------------
Gather Motion 3:1 (slice1; segments: 3) (cost=2.45..428.51 rows=17 width=24)
-> Hash Join (cost=2.45..428.29 rows=6 width=24)
Hash Cond: (t1.b = rt1.a)
-> Hash Join (cost=1.23..427.00 rows=6 width=16)
Hash Cond: (t1.b = rt3.a)
-> Seq Scan on t1 (cost=0.00..342.37 rows=33337 width=8)
-> Hash (cost=1.10..1.10 rows=10 width=8)
-> Seq Scan on rt3 (cost=0.00..1.10 rows=10 width=8)
-> Hash (cost=1.10..1.10 rows=10 width=8)
-> Seq Scan on rt1 (cost=0.00..1.10 rows=10 width=8)
Optimizer: Postgres query optimizer
(11 rows)
you can try this case, will got two range filters.
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| val = slot_getattr(slot, sk->sk_attno, &isnull); | ||
| if (isnull) |
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CREATE TABLE distinct_1(a int);
CREATE TABLE distinct_2(a int);
INSERT INTO distinct_1 VALUES(1),(2),(NULL);
INSERT INTO distinct_2 VALUES(1),(NULL);
SELECT * FROM distinct_1, distinct_2 WHERE distinct_1.a IS NOT DISTINCT FROM distinct_2.a;test got wrong result.
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I will fix it.
src/backend/executor/nodeSeqscan.c
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| return slot; | ||
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| if (node->filter_in_seqscan && node->filters && | ||
| !PassByBloomFilter(node, slot)) |
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tpcds 1TB, bloom filter will lose efficacy or create failed due to large rows ?
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Yes, when creating the Bloom filter, the system evaluates the estimated number of rows that this hash join will process and the amount of available memory during the execution plan generation. It determines whether using a Bloom filter for filtering data would be effective based on this evaluation. If it is assessed that the Bloom filter would not sufficiently enhance performance, then the Bloom filter will not be created.
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It determines whether using a Bloom filter for filtering data would be effective based on this evaluation
That makes sense, but where is related code, I just didn't see them in this pr.
Does it compares the number of rows between the output of hashtable and data in the probe table? If the rows of the hashtable are far less than that of the probe table , then use the runtime filter?
src/backend/executor/nodeHashjoin.c
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| { | ||
| match = false; | ||
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| if (!IsA(lfirst(lc), Var)) |
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Could it support other expression, whose one arg is the column attr, and the other is a const?
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I think that expressions like t1.c1 = 5 should be pushed down by the optimizer to operators such as SeqScan for early processing. Therefore, this feature does not handle expressions of the form t1.c1 = 5.
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Sorry, I didn't make it clear. I don't mean the predication on the var. like the below sql
EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF)
SELECT t1.c3 FROM t1, t2 WHERE t1.c2 = (t2.c2 + 10);
QUERY PLAN
-------------------------------------------------------------------------------------------
Gather Motion 3:1 (slice1; segments: 3) (actual rows=0 loops=1)
-> Hash Join (actual rows=0 loops=1)
Hash Cond: (t1.c2 = (t2.c2 + 10))
Extra Text: (seg2) Hash chain length 8.0 avg, 8 max, using 4 of 524288 buckets.
-> Seq Scan on t1 (actual rows=128 loops=1)
-> Hash (actual rows=32 loops=1)
Buckets: 524288 Batches: 1 Memory Usage: 4098kB
-> Seq Scan on t2 (actual rows=32 loops=1)
Optimizer: Postgres query optimizer
(9 rows)
As t2.c2 + 10 is not a Var but a T_OpExpr , the runtime filter cannot handle it.
Could we just iterate the expression tree and check if it only contains var and const ?
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Looks interesting. And I have some questions to discuss.
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src/backend/executor/nodeHashjoin.c
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| * result (hash filter) | ||
| * seqscan on t1, t1 is replicated table | ||
| */ | ||
| if (!IsA(child, HashJoinState) && !IsA(child, ResultState)) |
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Hash Join (cost=0.00..4019.55 rows=37 width=9) (actual time=3203.012..9927.435 rows=1399 loops=1)
Hash Cond: (web_sales_1_prt_2.ws_item_sk = item.i_item_sk)
Join Filter: (web_sales_1_prt_2.ws_ext_discount_amt > ((1.3 * avg(web_sales_1_prt_2_1.ws_ext_discount_amt))))
Rows Removed by Join Filter: 4763
Extra Text: (seg2) Hash chain length 1.0 avg, 1 max, using 198 of 2097152 buckets.
-> Append (cost=0.00..676.44 rows=2399189 width=13) (actual time=16.899..5572.473 rows=3090021 loops=1)
-> Seq Scan on web_sales_1_prt_2 (cost=0.00..676.44 rows=2399189 width=13) (actual time=16.895..1138.267 rows=662
149 loops=1)
-> Seq Scan on web_sales_1_prt_3 (cost=0.00..676.44 rows=2399189 width=13) (actual time=8.947..1102.409 rows=6621
36 loops=1)
-> Seq Scan on web_sales_1_prt_4 (cost=0.00..676.44 rows=2399189 width=13) (actual time=8.822..1100.839 rows=6621
48 loops=1)
-> Seq Scan on web_sales_1_prt_5 (cost=0.00..676.44 rows=2399189 width=13) (actual time=11.391..1083.785 rows=662
179 loops=1)
-> Seq Scan on web_sales_1_prt_6 (cost=0.00..676.44 rows=2399189 width=13) (actual time=13.030..649.141 rows=4414
09 loops=1)
-> Seq Scan on web_sales_1_prt_7 (cost=0.00..676.44 rows=2399189 width=13) (never executed)
-> Seq Scan on web_sales_1_prt_others (cost=0.00..676.44 rows=2399189 width=13) (actual time=1.213..3.203 rows=17
88 loops=1)
-> Hash (cost=2432.09..2432.09 rows=109 width=12) (actual time=3177.768..3177.770 rows=198 loops=1)
Buckets: 2097152 Batches: 1 Memory Usage: 16392kB
-> Broadcast Motion 3:3 (slice3; segments: 3) (cost=need to consider partitioned table .
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I will try.
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support partitioned table in c701092
src/backend/executor/nodeHash.c
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| attr_filter->min = LLONG_MAX; | ||
| attr_filter->max = LLONG_MIN; |
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LLONG_MAX, LLONG_MIN are platform-spec value, i.e. the bound value for unsigned long long, which may not be exactly the same width as Datum. For safety, static assert could be considered.
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I see StaticAssertDecl(SIZEOF_DATUM == 8, "sizeof datum is not 8"); in postgres.h, so it's better to use INT64_MAX/INT64_MIN here.
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use LONG_MAX, LONG_MIN instead ?
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fix with 99eabb2
src/backend/executor/nodeHashjoin.c
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| /* | ||
| * Only applicatable for inner, right and semi join, | ||
| */ |
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Could you give a little more explain about why these join types are supported and others are not?
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Add more message to explain why just inner, right and semi join are allowed with runtime filter.
fix it in 98dac6d
src/backend/executor/nodeHashjoin.c
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| if (!IsA(expr, OpExpr) && !IsA(expr, FuncExpr)) | ||
| return false; |
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These 2 lines duplicate with the following if-elseif-else code, could be deleted.
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fix with 99eabb2
src/backend/executor/nodeHashjoin.c
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| break; | ||
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| var = lfirst(lc); | ||
| if (var->varno == INNER_VAR) | ||
| *rattno = var->varattno; | ||
| else if (var->varno == OUTER_VAR) | ||
| *lattno = var->varattno; | ||
| else | ||
| break; | ||
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| match = true; | ||
| } | ||
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| return match; |
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The match flag gets the code hard(several modifications) to read. The break statement could be replaced by return false;. If the foreach loop ends, all conditions match, so returns true.
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use the more intuitive way to refactor the code, like below
/* check the first arg */
...
/* check the second arg */
...
return true;
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fix with 99eabb2
src/backend/executor/nodeSeqscan.c
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| if (TupIsNull(slot)) | ||
| return slot; |
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It seems that slot is never NULL here, so Assert(!TupIsNull(slot)); is better or remove them.
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fix with 99eabb2
| /* | ||
| * SK_EMPYT means the end of the array of the ScanKey | ||
| */ | ||
| sk[*num].sk_flags = SK_EMPYT; |
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How to check the boundary of the ScanKey array in rescan? In normal rescan, the number of ScanKeys is the same as begin_scan. If the number of ScanKeys is larger in rescan than that in begin_scan, the boundary value might be invalid and dangerous to access.
+----------+ AttrFilter +------+ ScanKey +------------+
| HashJoin | ------------> | Hash | ---------> | SeqScan/AM |
+----------+ +------+ +------------+
If "gp_enable_runtime_filter_pushdown" is on, three steps will be run:
Step 1. In ExecInitHashJoin(), try to find the mapper between the var in
hashclauses and the var in SeqScan. If found we will save the mapper in
AttrFilter and push them to Hash node;
Step 2. We will create the range/bloom filters in AttrFilter during building
hash table, and these filters will be converted to the list of ScanKey
and pushed down to Seqscan when the building finishes;
Step 3. If AM support SCAN_SUPPORT_RUNTIME_FILTER, these ScanKeys will be pushed
down to the AM module further, otherwise will be used to filter slot in
Seqscan;
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There are codes changed in MultiExecParallelHash, please add some parallel tests with runtime filter. |
got it. |
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Hi, with gp_enable_runtime_filter_pushdown = on, execute SQL below will get a crash: gpadmin=# show gp_enable_runtime_filter_pushdown;
gp_enable_runtime_filter_pushdown
-----------------------------------
on
(1 row)CREATE TABLE test_tablesample (dist int, id int, name text) WITH (fillfactor=10) DISTRIBUTED BY (dist);
-- use fillfactor so we don't have to load too much data to get multiple pages
-- Changed the column length in order to match the expected results based on relation's blocksz
INSERT INTO test_tablesample SELECT 0, i, repeat(i::text, 875) FROM generate_series(0, 9) s(i) ORDER BY i;
INSERT INTO test_tablesample SELECT 3, i, repeat(i::text, 875) FROM generate_series(10, 19) s(i) ORDER BY i;
INSERT INTO test_tablesample SELECT 5, i, repeat(i::text, 875) FROM generate_series(20, 29) s(i) ORDER BY i;
EXPLAIN (COSTS OFF)
SELECT id FROM test_tablesample TABLESAMPLE SYSTEM (50) REPEATABLE (2);
FATAL: Unexpected internal error (assert.c:48)
DETAIL: FailedAssertion("IsA(planstate, SeqScanState)", File: "explain.c", Line: 4154)
server closed the connection unexpectedly
This probably means the server terminated abnormally
before or while processing the request.
The connection to the server was lost. Attempting reset: Succeeded.
psql (14.4, server 14.4)
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Thanks, I'll reproduce the issue and fix it. |
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Thanks for your detailed explanation.
Make sense. When doing hashjoin, index scan or index only scan are often not used on probe node.
Exactly, and if there is any lock used to solve the problem may even lead bad performance. |
runtime_filter has been pushed down to t3 table seqscan, but 'explain analyze' doesn't print them out. |
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Thanks for your test case. Based on these, I rewrote code to ensure that debug info are always displayed even when the number of filtered rows is zero. And add the test case into gp_runtime_filter.sql too. |
Thanks for your test case. I fix it in 98dac6d And add the test case into gp_runtime_filter.sql too. |
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Hi @zhangyue-hashdata Asking mostly out of curiosity, I see here are quite a few reviewers here already :) |
Basically, you're correct. Because our goal is to filter out as much data as possible right at the point of data generation. However, this will lead to very complex evaluations, so we only made a simple estimation based on rows and work memory when creating the Bloom filter. |
fix it in 7ab040a |
src/backend/executor/nodeSeqscan.c
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| if (table_scan_getnextslot(scandesc, direction, slot)) | ||
| while (table_scan_getnextslot(scandesc, direction, slot)) | ||
| { | ||
| if (node->filter_in_seqscan && node->filters && |
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if (!node->filter_in_seqscan || !node->filters)
{
if (table_scan_getnextslot(scandesc, direction, slot))
return slot;
}
else
{
while (table_scan_getnextslot(scandesc, direction, slot))
{
.....
}
}this make origin path more efficient and readable ?
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good idea! I fix in bcf93e6
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from tpcds 10s details table, there are some bad cases. |
+----------+ AttrFilter +------+ ScanKey +------------+
| HashJoin | ------------> | Hash | ---------> | SeqScan/AM |
+----------+ +------+ +------------+
If "gp_enable_runtime_filter_pushdown" is on, three steps will be run:
Step 1. In ExecInitHashJoin(), try to find the mapper between the var in
hashclauses and the var in SeqScan. If found we will save the mapper in
AttrFilter and push them to Hash node;
Step 2. We will create the range/bloom filters in AttrFilter during building
hash table, and these filters will be converted to the list of ScanKey
and pushed down to Seqscan when the building finishes;
Step 3. If AM support SCAN_SUPPORT_RUNTIME_FILTER, these ScanKeys will be pushed
down to the AM module further, otherwise will be used to filter slot in
Seqscan;
perf:
CPU E5-2680 v2 10 cores, memory 32GB, 3 segments
tpcds 10s details
Fixes #ISSUE_Number
What does this PR do?
Type of Change
Breaking Changes
Test Plan
make installcheckmake -C src/test installcheck-cbdb-parallelImpact
Performance:
User-facing changes:
Dependencies:
Checklist
Additional Context
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