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Positioned UPDATE statement prohibits index usage for the subsequent cursor field references [CORE4447] #4767

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firebird-issue-importer opened this issue Jun 2, 2014 · 6 comments

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firebird-issue-importer commented Jun 2, 2014

Submitted by: @pavel-zotov

LI-T6.3.0.31152

DDL:

recreate table ts(id int, x int, y int, z int, constraint ts_pk_id primary key (id) );
recreate table tt(x int, y int, z int, constraint tt_pk_xy primary key (x,y) );
commit;

insert into ts
select row_number()over(), rand()*10, rand()*10, rand()*10
from rdb$types;
commit;

insert into tt select distinct x,y,0 from ts;
commit;

Tests.

var-1.

execute block as
begin
for select id,x,y,z from ts as cursor c
do begin
update ts set id = id where id = http://c.id; -- <<<<<<<<<<<<<< ::: NB ::: we lock record in source using it's PK
update tt t set t.z = t.z + c.z where t.x=c.x and t.y = c.y;
end
end

Trace:

PLAN (TS INDEX (TS_PK_ID))
PLAN (T INDEX (TT_PK_XY))
PLAN (C TS NATURAL)
0 records fetched
5 ms, 6341 fetch(es), 1010 mark(s)

Table Natural Index Update
*************************************************************
TS 252 252 252
TT 252 252

-- OK, only INDEXED reads for table TT in this sample.

var-2.

execute block as
begin
for select id,x,y,z from ts as cursor c
do begin
update ts set id = id where current of c; -- <<<<<<<<<<<<<<< ::: NB ::: we lock record in source using "current of" clause
update tt t set t.z = t.z + c.z where t.x=c.x and t.y = c.y;
end
end

Trace:
PLAN (T NATURAL)
PLAN (C TS NATURAL)
0 records fetched
25 ms, 56489 fetch(es), 1010 mark(s)

Table Natural Index Update
**************************************************************
TS 252 252
TT 25704 252

Here we get over 25'000 NATURAL reads of table TT and almost 56500 fetches.
The only difference between var-1 and var-2 is the way which is used to lock records in the SOURCE table (TS) rather than target one.

Commits: ec07db9 FirebirdSQL/fbt-repository@6c4c72b

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firebird-issue-importer commented Jun 2, 2014

Modified by: @dyemanov

assignee: Dmitry Yemanov [ dimitr ]

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firebird-issue-importer commented Jun 4, 2014

Modified by: @dyemanov

summary: Indices are ignored on table which receives data processed inside cursor when using "AS CURSOR <cursor_name>" clause and lock source record using "WHERE CURRENT OF <cursor_name>" => Positioned update/delete prohibits index usage for the subsequent cursor field references

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firebird-issue-importer commented Jun 4, 2014

Modified by: @dyemanov

summary: Positioned update/delete prohibits index usage for the subsequent cursor field references => Positioned UPDATE statement prohibits index usage for the subsequent cursor field references

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firebird-issue-importer commented Jun 4, 2014

Modified by: @dyemanov

status: Open [ 1 ] => Resolved [ 5 ]

resolution: Fixed [ 1 ]

Fix Version: 3.0 Beta 1 [ 10332 ]

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firebird-issue-importer commented May 30, 2015

Modified by: @pavel-zotov

status: Resolved [ 5 ] => Resolved [ 5 ]

QA Status: Done successfully

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firebird-issue-importer commented Sep 23, 2015

Modified by: @pcisar

status: Resolved [ 5 ] => Closed [ 6 ]

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