Comments (2)
ashwinstar
commented on June 27, 2024
(not based on actual debugging the code... surface code browsing) The callers to EOXactListAdd() are RelationBuildLocalRelation() and RelationSetNewRelfilenode(). Both will only be called for writer gang QE and not reader gang QE. Hence, eoxact_list will not be populated for reader QEs. Hence can't use eoxact_list or eoxact_list_overflowed for reader QEs to perform targeted cleanup of Relcache. That's the reason current behavior is to clean full relcache based on hashtable acting similar to overflow case.
If really wish to optimize then might have to look into ways to pass this info from QE Writers to QE readers. Above example query I expect will only execute in QE writer and doesn't need slices, it will not even have why DTX_CONTEXT_QE_READER. Instead it will be DTX_CONTEXT_QE_AUTO_COMMIT_IMPLICIT. So I am missing it will not even flow through the case you mentioned. Please can you explain more and with evidence clarify the situation more.
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maliangzhu
commented on June 27, 2024
Sorry, my case has some mistake . only select * from t1 will not scan heap again. The actural case has motion like this:
postgres=# select * from t1,t2;
WARNING: no index (seg2 slice2 10.10.2.165:6002 pid=3631)
WARNING: no index (seg0 slice2 10.10.2.165:6000 pid=3630)
WARNING: no index (seg1 slice2 10.10.2.165:6001 pid=3632)
a | b
---+---
(0 rows)
postgres=# select * from t1,t2;
WARNING: no index (seg1 slice2 10.10.2.165:6001 pid=3632)
WARNING: no index (seg0 slice2 10.10.2.165:6000 pid=3630)
WARNING: no index (seg2 slice2 10.10.2.165:6002 pid=3631)
a | b
---+---
(0 rows)
postgres=# explain select * from t1,t2;
QUERY PLAN
---------------------------------------------------------------------------------------------
Gather Motion 3:1 (slice1; segments: 3) (cost=0.00..1324032.11 rows=1 width=8)
-> Nested Loop (cost=0.00..1324032.11 rows=1 width=8)
Join Filter: true
-> Broadcast Motion 3:3 (slice2; segments: 3) (cost=0.00..431.00 rows=1 width=4)
-> Seq Scan on t1 (cost=0.00..431.00 rows=1 width=4)
-> Seq Scan on t2 (cost=0.00..431.00 rows=1 width=4)
Optimizer: GPORCA
(7 rows)
postgres=# select version();
version
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
-------
PostgreSQL 12.12 (Greenplum Database 7.2.0-rc.1+dev.58.g0d1c4aa361 build dev) on x86_64-pc-linux-gnu, compiled by gcc (GCC) 8.3.1 20190311 (Red Hat 8.3.1-3), 64-bit compiled on May 10 2024 22:05:50 Bhuvn
esh C.
(1 row)I added some code that can show "no index"
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 42aaa5bad6..6298d20a6f 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -468,6 +468,7 @@ systable_getnext(SysScanDesc sysscan)
}
else
{
+ elog(WARNING,"no index");
if (table_scan_getnextslot(sysscan->scan, ForwardScanDirection, sysscan->slot))
{
bool shouldFree;from gpdb.
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