Hmmmm. With the current head of trunk ...
I run this and the recursive version takes 93 milliseconds vs the iterative
version which takes 203 milliseconds.
Creating all possible covering indexes takes 110 milliseconds vs 141
milliseconds.
Creating only used/required covering indexes takes 93 milliseconds vs 124
milliseconds
Can you add .timer on and .eqp on and see if you are getting reasonable query
plans? Also, what version of SQLite are you using?
Is the version you are using creating the necessary automatic covering indexes?
If I manually create indexes I get better and worse results, as expected.
Those follow after these runs.
>timethis "sqlite64 graph.db < GRAPH-performance-Load.sql"
TimeThis : Command Line : sqlite64 graph.db < GRAPH-performance-Load.sql
TimeThis : Start Time : Thu Feb 16 06:47:14 2017
TimeThis : Command Line : sqlite64 graph.db < GRAPH-performance-Load.sql
TimeThis : Start Time : Thu Feb 16 06:47:14 2017
TimeThis : End Time : Thu Feb 16 06:47:14 2017
TimeThis : Elapsed Time : 00:00:00.078
>dir graph.db
2017-02-16 06:47 45,056 graph.db
>timethis "sqlite64 graph.db < GRAPH-performance-recursive.sql"
TimeThis : Command Line : sqlite64 graph.db < GRAPH-performance-recursive.sql
TimeThis : Start Time : Thu Feb 16 06:47:58 2017
SQLite 3.18.0 2017-02-15 22:36:15 58797e9bafa95709e0f706a15f42f93b409e2db5
.eqp on
.timer on
update GRAPH
set Level = null;
--EQP-- 0,0,0,SCAN TABLE GRAPH
Run Time: real 0.016 user 0.000000 sys 0.000000
with
HIERARCHY (FromID,ToID,Level) as
(
select Parent,
Child,
'0'
from GRAPH
where Parent is null
union all
select H.ToID,
G.Child,
H.Level + 1
from HIERARCHY H,
GRAPH G
where H.ToID = G.Parent
)
update GRAPH
set Level = (select Level
from HIERARCHY H
where ToID = GRAPH.Child);
--EQP-- 0,0,0,SCAN TABLE GRAPH
--EQP-- 0,0,0,EXECUTE CORRELATED SCALAR SUBQUERY 0
--EQP-- 2,0,0,SCAN TABLE GRAPH
--EQP-- 3,0,0,SCAN TABLE HIERARCHY AS H
--EQP-- 3,1,1,SEARCH TABLE GRAPH AS G USING AUTOMATIC COVERING INDEX (Parent=?)
--EQP-- 1,0,0,COMPOUND SUBQUERIES 0 AND 0 (UNION ALL)
--EQP-- 0,0,0,SEARCH SUBQUERY 1 AS H USING AUTOMATIC COVERING INDEX (ToID=?)
Run Time: real 0.046 user 0.000000 sys 0.015625
select Level,
count(*) as Number
from GRAPH
group by Level;
--EQP-- 0,0,0,SCAN TABLE GRAPH
--EQP-- 0,0,0,USE TEMP B-TREE FOR GROUP BY
0|1
1|47
2|215
3|638
4|1010
5|729
6|50
Run Time: real 0.000 user 0.000000 sys 0.000000
TimeThis : Command Line : sqlite64 graph.db < GRAPH-performance-recursive.sql
TimeThis : Start Time : Thu Feb 16 06:47:58 2017
TimeThis : End Time : Thu Feb 16 06:47:58 2017
TimeThis : Elapsed Time : 00:00:00.093
>timethis "sqlite64 graph.db < GRAPH-performance-iterative.sql"
TimeThis : Command Line : sqlite64 graph.db < GRAPH-performance-iterative.sql
TimeThis : Start Time : Thu Feb 16 06:48:10 2017
SQLite 3.18.0 2017-02-15 22:36:15 58797e9bafa95709e0f706a15f42f93b409e2db5
.eqp on
.timer on
update GRAPH
set Level = null;
--EQP-- 0,0,0,SCAN TABLE GRAPH
Run Time: real 0.031 user 0.000000 sys 0.015625
update GRAPH
set Level = 0
where Parent is null;
--EQP-- 0,0,0,SCAN TABLE GRAPH
Run Time: real 0.015 user 0.000000 sys 0.000000
update GRAPH
set Level = 1
where Parent in (select Child
from GRAPH
where Level = 0);
--EQP-- 0,0,0,SCAN TABLE GRAPH
--EQP-- 0,0,0,EXECUTE LIST SUBQUERY 0
--EQP-- 0,0,0,SCAN TABLE GRAPH
Run Time: real 0.016 user 0.000000 sys 0.000000
update GRAPH
set Level = 2
where Parent in (select Child
from GRAPH
where Level = 1);
--EQP-- 0,0,0,SCAN TABLE GRAPH
--EQP-- 0,0,0,EXECUTE LIST SUBQUERY 0
--EQP-- 0,0,0,SCAN TABLE GRAPH
Run Time: real 0.015 user 0.015625 sys 0.000000
update GRAPH
set Level = 3
where Parent in (select Child
from GRAPH
where Level = 2);
--EQP-- 0,0,0,SCAN TABLE GRAPH
--EQP-- 0,0,0,EXECUTE LIST SUBQUERY 0
--EQP-- 0,0,0,SCAN TABLE GRAPH
Run Time: real 0.032 user 0.015625 sys 0.000000
update GRAPH
set Level = 4
where Parent in (select Child
from GRAPH
where Level = 3);
--EQP-- 0,0,0,SCAN TABLE GRAPH
--EQP-- 0,0,0,EXECUTE LIST SUBQUERY 0
--EQP-- 0,0,0,SCAN TABLE GRAPH
Run Time: real 0.015 user 0.000000 sys 0.000000
update GRAPH
set Level = 5
where Parent in (select Child
from GRAPH
where Level = 4);
--EQP-- 0,0,0,SCAN TABLE GRAPH
--EQP-- 0,0,0,EXECUTE LIST SUBQUERY 0
--EQP-- 0,0,0,SCAN TABLE GRAPH
Run Time: real 0.016 user 0.000000 sys 0.000000
update GRAPH
set Level = 6
where Parent in (select Child
from GRAPH
where Level = 5);
--EQP-- 0,0,0,SCAN TABLE GRAPH
--EQP-- 0,0,0,EXECUTE LIST SUBQUERY 0
--EQP-- 0,0,0,SCAN TABLE GRAPH
Run Time: real 0.016 user 0.000000 sys 0.000000
select Level,
count(*) as Number
from GRAPH
group by Level;
--EQP-- 0,0,0,SCAN TABLE GRAPH
--EQP-- 0,0,0,USE TEMP B-TREE FOR GROUP BY
0|1
1|47
2|215
3|638
4|1010
5|729
6|50
Run Time: real 0.015 user 0.000000 sys 0.000000
TimeThis : Command Line : sqlite64 graph.db < GRAPH-performance-iterative.sql
TimeThis : Start Time : Thu Feb 16 06:48:10 2017
TimeThis : End Time : Thu Feb 16 06:48:10 2017
TimeThis : Elapsed Time : 00:00:00.203
If I manually add the required covering indexes (actually, I added all possible
ones to the end of -Load so the query planner can decide what to do; and also
added all the updates in the -Iterative version into a single transaction to
more closely reflect that the -recursive version is running only a single
update transaction; and put all the inserts in the -Load into a single
transaction so that they occur on milliseconds), the results are closer
together, but the recursive version still wins at 110 milliseconds vs 141 for
the iterative. (The recusive increased due to the requirement to maintain more
indexes, and the iterative was faster because it now had indexes to use (but
could have been faster without the excess unused indexes)).
>timethis "sqlite64 graph.db < GRAPH-performance-Load.sql"
TimeThis : Command Line : sqlite64 graph.db < GRAPH-performance-Load.sql
TimeThis : Start Time : Thu Feb 16 07:05:55 2017
create table GRAPH
(
Parent integer,
Child integer,
Level integer
);
.echo off
create index Covering1 on Graph (Parent, Child, Level);
create index Covering2 on Graph (Child, Parent, Level);
create index Covering3 on Graph (Level, Parent, Child);
create index Covering4 on Graph (Level, Child, Parent);
analyze;
TimeThis : Command Line : sqlite64 graph.db < GRAPH-performance-Load.sql
TimeThis : Start Time : Thu Feb 16 07:05:55 2017
TimeThis : End Time : Thu Feb 16 07:05:55 2017
TimeThis : Elapsed Time : 00:00:00.140
>timethis "sqlite64 graph.db < GRAPH-performance-recursive.sql"
TimeThis : Command Line : sqlite64 graph.db < GRAPH-performance-recursive.sql
TimeThis : Start Time : Thu Feb 16 07:06:16 2017
SQLite 3.18.0 2017-02-15 22:36:15 58797e9bafa95709e0f706a15f42f93b409e2db5
.eqp on
.timer on
update GRAPH
set Level = null;
--EQP-- 0,0,0,SCAN TABLE GRAPH
Run Time: real 0.032 user 0.000000 sys 0.015625
with
HIERARCHY (FromID,ToID,Level) as
(
select Parent,
Child,
'0'
from GRAPH
where Parent is null
union all
select H.ToID,
G.Child,
H.Level + 1
from HIERARCHY H,
GRAPH G
where H.ToID = G.Parent
)
update GRAPH
set Level = (select Level
from HIERARCHY H
where ToID = GRAPH.Child);
--EQP-- 0,0,0,SCAN TABLE GRAPH
--EQP-- 0,0,0,EXECUTE CORRELATED SCALAR SUBQUERY 0
--EQP-- 2,0,0,SEARCH TABLE GRAPH USING COVERING INDEX Covering1 (Parent=?)
--EQP-- 3,0,0,SCAN TABLE HIERARCHY AS H
--EQP-- 3,1,1,SEARCH TABLE GRAPH AS G USING COVERING INDEX Covering1 (Parent=?)
--EQP-- 1,0,0,COMPOUND SUBQUERIES 0 AND 0 (UNION ALL)
--EQP-- 0,0,0,SEARCH SUBQUERY 1 AS H USING AUTOMATIC COVERING INDEX (ToID=?)
Run Time: real 0.047 user 0.015625 sys 0.015625
select Level,
count(*) as Number
from GRAPH
group by Level;
--EQP-- 0,0,0,SCAN TABLE GRAPH USING COVERING INDEX Covering4
0|1
1|47
2|215
3|638
4|1010
5|729
6|50
Run Time: real 0.000 user 0.000000 sys 0.000000
TimeThis : Command Line : sqlite64 graph.db < GRAPH-performance-recursive.sql
TimeThis : Start Time : Thu Feb 16 07:06:16 2017
TimeThis : End Time : Thu Feb 16 07:06:16 2017
TimeThis : Elapsed Time : 00:00:00.110
>timethis "sqlite64 graph.db < GRAPH-performance-iterative.sql"
TimeThis : Command Line : sqlite64 graph.db < GRAPH-performance-iterative.sql
TimeThis : Start Time : Thu Feb 16 07:06:24 2017
SQLite 3.18.0 2017-02-15 22:36:15 58797e9bafa95709e0f706a15f42f93b409e2db5
.eqp on
.timer on
update GRAPH
set Level = null;
--EQP-- 0,0,0,SCAN TABLE GRAPH
Run Time: real 0.047 user 0.031250 sys 0.015625
begin;
Run Time: real 0.000 user 0.000000 sys 0.000000
update GRAPH
set Level = 0
where Parent is null;
--EQP-- 0,0,0,SEARCH TABLE GRAPH USING INDEX Covering1 (Parent=?)
Run Time: real 0.000 user 0.000000 sys 0.000000
update GRAPH
set Level = 1
where Parent in (select Child
from GRAPH
where Level = 0);
--EQP-- 0,0,0,SEARCH TABLE GRAPH USING INDEX Covering1 (Parent=?)
--EQP-- 0,0,0,EXECUTE LIST SUBQUERY 0
--EQP-- 0,0,0,SEARCH TABLE GRAPH USING COVERING INDEX Covering4 (Level=?)
Run Time: real 0.000 user 0.000000 sys 0.000000
update GRAPH
set Level = 2
where Parent in (select Child
from GRAPH
where Level = 1);
--EQP-- 0,0,0,SEARCH TABLE GRAPH USING INDEX Covering1 (Parent=?)
--EQP-- 0,0,0,EXECUTE LIST SUBQUERY 0
--EQP-- 0,0,0,SEARCH TABLE GRAPH USING COVERING INDEX Covering4 (Level=?)
Run Time: real 0.000 user 0.000000 sys 0.000000
update GRAPH
set Level = 3
where Parent in (select Child
from GRAPH
where Level = 2);
--EQP-- 0,0,0,SEARCH TABLE GRAPH USING INDEX Covering1 (Parent=?)
--EQP-- 0,0,0,EXECUTE LIST SUBQUERY 0
--EQP-- 0,0,0,SEARCH TABLE GRAPH USING COVERING INDEX Covering4 (Level=?)
Run Time: real 0.016 user 0.015625 sys 0.000000
update GRAPH
set Level = 4
where Parent in (select Child
from GRAPH
where Level = 3);
--EQP-- 0,0,0,SEARCH TABLE GRAPH USING INDEX Covering1 (Parent=?)
--EQP-- 0,0,0,EXECUTE LIST SUBQUERY 0
--EQP-- 0,0,0,SEARCH TABLE GRAPH USING COVERING INDEX Covering4 (Level=?)
Run Time: real 0.000 user 0.000000 sys 0.000000
update GRAPH
set Level = 5
where Parent in (select Child
from GRAPH
where Level = 4);
--EQP-- 0,0,0,SEARCH TABLE GRAPH USING INDEX Covering1 (Parent=?)
--EQP-- 0,0,0,EXECUTE LIST SUBQUERY 0
--EQP-- 0,0,0,SEARCH TABLE GRAPH USING COVERING INDEX Covering4 (Level=?)
Run Time: real 0.015 user 0.000000 sys 0.000000
update GRAPH
set Level = 6
where Parent in (select Child
from GRAPH
where Level = 5);
--EQP-- 0,0,0,SEARCH TABLE GRAPH USING INDEX Covering1 (Parent=?)
--EQP-- 0,0,0,EXECUTE LIST SUBQUERY 0
--EQP-- 0,0,0,SEARCH TABLE GRAPH USING COVERING INDEX Covering4 (Level=?)
Run Time: real 0.000 user 0.000000 sys 0.000000
commit;
Run Time: real 0.016 user 0.000000 sys 0.000000
select Level,
count(*) as Number
from GRAPH
group by Level;
--EQP-- 0,0,0,SCAN TABLE GRAPH USING COVERING INDEX Covering4
0|1
1|47
2|215
3|638
4|1010
5|729
6|50
Run Time: real 0.015 user 0.015625 sys 0.000000
TimeThis : Command Line : sqlite64 graph.db < GRAPH-performance-iterative.sql
TimeThis : Start Time : Thu Feb 16 07:06:24 2017
TimeThis : End Time : Thu Feb 16 07:06:24 2017
TimeThis : Elapsed Time : 00:00:00.141
Creating only the required index (Covering1 and Covering4) results in the
changes anticipated, but the recursive version still wins by a smaller margin:
93 milliseconds vs 124 milliseconds.
>timethis "sqlite64 graph.db < GRAPH-performance-Load.sql"
TimeThis : Command Line : sqlite64 graph.db < GRAPH-performance-Load.sql
TimeThis : Start Time : Thu Feb 16 07:22:19 2017
create table GRAPH
(
Parent integer,
Child integer,
Level integer
);
.echo off
create index Covering1 on Graph (Parent, Child, Level);
create index Covering4 on Graph (Level, Child, Parent);
analyze;
TimeThis : Command Line : sqlite64 graph.db < GRAPH-performance-Load.sql
TimeThis : Start Time : Thu Feb 16 07:22:19 2017
TimeThis : End Time : Thu Feb 16 07:22:19 2017
TimeThis : Elapsed Time : 00:00:00.109
>timethis "sqlite64 graph.db < GRAPH-performance-recursive.sql"
TimeThis : Command Line : sqlite64 graph.db < GRAPH-performance-recursive.sql
TimeThis : Start Time : Thu Feb 16 07:22:24 2017
SQLite 3.18.0 2017-02-15 22:36:15 58797e9bafa95709e0f706a15f42f93b409e2db5
.eqp on
.timer on
update GRAPH
set Level = null;
--EQP-- 0,0,0,SCAN TABLE GRAPH
Run Time: real 0.031 user 0.000000 sys 0.000000
with
HIERARCHY (FromID,ToID,Level) as
(
select Parent,
Child,
'0'
from GRAPH
where Parent is null
union all
select H.ToID,
G.Child,
H.Level + 1
from HIERARCHY H,
GRAPH G
where H.ToID = G.Parent
)
update GRAPH
set Level = (select Level
from HIERARCHY H
where ToID = GRAPH.Child);
--EQP-- 0,0,0,SCAN TABLE GRAPH
--EQP-- 0,0,0,EXECUTE CORRELATED SCALAR SUBQUERY 0
--EQP-- 2,0,0,SEARCH TABLE GRAPH USING COVERING INDEX Covering1 (Parent=?)
--EQP-- 3,0,0,SCAN TABLE HIERARCHY AS H
--EQP-- 3,1,1,SEARCH TABLE GRAPH AS G USING COVERING INDEX Covering1 (Parent=?)
--EQP-- 1,0,0,COMPOUND SUBQUERIES 0 AND 0 (UNION ALL)
--EQP-- 0,0,0,SEARCH SUBQUERY 1 AS H USING AUTOMATIC COVERING INDEX (ToID=?)
Run Time: real 0.032 user 0.000000 sys 0.015625
select Level,
count(*) as Number
from GRAPH
group by Level;
--EQP-- 0,0,0,SCAN TABLE GRAPH USING COVERING INDEX Covering4
0|1
1|47
2|215
3|638
4|1010
5|729
6|50
Run Time: real 0.000 user 0.000000 sys 0.000000
TimeThis : Command Line : sqlite64 graph.db < GRAPH-performance-recursive.sql
TimeThis : Start Time : Thu Feb 16 07:22:24 2017
TimeThis : End Time : Thu Feb 16 07:22:24 2017
TimeThis : Elapsed Time : 00:00:00.093
>timethis "sqlite64 graph.db < GRAPH-performance-iterative.sql"
TimeThis : Command Line : sqlite64 graph.db < GRAPH-performance-iterative.sql
TimeThis : Start Time : Thu Feb 16 07:22:28 2017
SQLite 3.18.0 2017-02-15 22:36:15 58797e9bafa95709e0f706a15f42f93b409e2db5
.eqp on
.timer on
update GRAPH
set Level = null;
--EQP-- 0,0,0,SCAN TABLE GRAPH
Run Time: real 0.031 user 0.015625 sys 0.000000
begin;
Run Time: real 0.000 user 0.000000 sys 0.000000
update GRAPH
set Level = 0
where Parent is null;
--EQP-- 0,0,0,SEARCH TABLE GRAPH USING INDEX Covering1 (Parent=?)
Run Time: real 0.000 user 0.000000 sys 0.000000
update GRAPH
set Level = 1
where Parent in (select Child
from GRAPH
where Level = 0);
--EQP-- 0,0,0,SEARCH TABLE GRAPH USING INDEX Covering1 (Parent=?)
--EQP-- 0,0,0,EXECUTE LIST SUBQUERY 0
--EQP-- 0,0,0,SEARCH TABLE GRAPH USING COVERING INDEX Covering4 (Level=?)
Run Time: real 0.000 user 0.000000 sys 0.000000
update GRAPH
set Level = 2
where Parent in (select Child
from GRAPH
where Level = 1);
--EQP-- 0,0,0,SEARCH TABLE GRAPH USING INDEX Covering1 (Parent=?)
--EQP-- 0,0,0,EXECUTE LIST SUBQUERY 0
--EQP-- 0,0,0,SEARCH TABLE GRAPH USING COVERING INDEX Covering4 (Level=?)
Run Time: real 0.000 user 0.000000 sys 0.000000
update GRAPH
set Level = 3
where Parent in (select Child
from GRAPH
where Level = 2);
--EQP-- 0,0,0,SEARCH TABLE GRAPH USING INDEX Covering1 (Parent=?)
--EQP-- 0,0,0,EXECUTE LIST SUBQUERY 0
--EQP-- 0,0,0,SEARCH TABLE GRAPH USING COVERING INDEX Covering4 (Level=?)
Run Time: real 0.000 user 0.000000 sys 0.000000
update GRAPH
set Level = 4
where Parent in (select Child
from GRAPH
where Level = 3);
--EQP-- 0,0,0,SEARCH TABLE GRAPH USING INDEX Covering1 (Parent=?)
--EQP-- 0,0,0,EXECUTE LIST SUBQUERY 0
--EQP-- 0,0,0,SEARCH TABLE GRAPH USING COVERING INDEX Covering4 (Level=?)
Run Time: real 0.016 user 0.015625 sys 0.000000
update GRAPH
set Level = 5
where Parent in (select Child
from GRAPH
where Level = 4);
--EQP-- 0,0,0,SEARCH TABLE GRAPH USING INDEX Covering1 (Parent=?)
--EQP-- 0,0,0,EXECUTE LIST SUBQUERY 0
--EQP-- 0,0,0,SEARCH TABLE GRAPH USING COVERING INDEX Covering4 (Level=?)
Run Time: real 0.000 user 0.000000 sys 0.000000
update GRAPH
set Level = 6
where Parent in (select Child
from GRAPH
where Level = 5);
--EQP-- 0,0,0,SEARCH TABLE GRAPH USING INDEX Covering1 (Parent=?)
--EQP-- 0,0,0,EXECUTE LIST SUBQUERY 0
--EQP-- 0,0,0,SEARCH TABLE GRAPH USING COVERING INDEX Covering4 (Level=?)
Run Time: real 0.000 user 0.000000 sys 0.000000
commit;
Run Time: real 0.015 user 0.000000 sys 0.000000
select Level,
count(*) as Number
from GRAPH
group by Level;
--EQP-- 0,0,0,SCAN TABLE GRAPH USING COVERING INDEX Covering4
0|1
1|47
2|215
3|638
4|1010
5|729
6|50
Run Time: real 0.016 user 0.000000 sys 0.000000
TimeThis : Command Line : sqlite64 graph.db < GRAPH-performance-iterative.sql
TimeThis : Start Time : Thu Feb 16 07:22:28 2017
TimeThis : End Time : Thu Feb 16 07:22:28 2017
TimeThis : Elapsed Time : 00:00:00.124
> -----Original Message-----
> From: sqlite-users [mailto:sqlite-users-boun...@mailinglists.sqlite.org]
> On Behalf Of Jean-Luc Hainaut
> Sent: Thursday, 16 February, 2017 05:57
> To: SQLite mailing list
> Subject: [sqlite] About the performance of recursive WITH
>
> Hi,
>
> This post concerns a strange (imho) behaviour of recursive WITH update
> query as far as execution time is concerned.
>
> I have created (in an "In memory" DB) a table that stores a set of nodes
> arranged in a tree structure (actually the skeleton of the contents of a
> Windows folder):
>
> create table GRAPH(Parent int, Child int, Level int);
>
> Column "Level" indicates the depth of the node in the tree. The root
> node has Level 0, its children Level 1, and so on.
>
> 2690 nodes have been inserted, with "Level" initialized to null:
>
> insert into GRAPH(Parent,Child) values (null,1); -- root node (no
> parent)
> insert into GRAPH(Parent,Child) values (1,9); -- child of the
> root node
> insert into GRAPH(Parent,Child) values (9,10); -- grand-child of
> the root node
> insert into GRAPH(Parent,Child) values (9,11);
> insert into GRAPH(Parent,Child) values (9,12);
> insert into GRAPH(Parent,Child) values (9,13);
> etc.
>
> Considering the size of the table, no indexes have been created.
> The distribution of nodes among the levels is fairly "normal":
>
> +-------+--------+
> | Level | Number |
> +-------+--------+
> | 0 | 1 |
> | 1 | 47 |
> | 2 | 215 |
> | 3 | 638 |
> | 4 | 1010 |
> | 5 | 729 |
> | 6 | 50 |
> +-------+--------+
>
> Now, I would like to compute the "Level" value of all nodes from their
> position in the tree. This task immediately suggests a recursive WITH
> update:
>
> with recursive
> HIERARCHY(FromID,ToID,Level) as
> (
> select Parent, Child, '0'
> from GRAPH where Parent is null
> union all
> select H.ToID, G.Child, H.Level + 1
> from HIERARCHY H, GRAPH G
> where H.ToID = G.Parent
> )
> update GRAPH
> set Level = (select Level from HIERARCHYwhere ToID = GRAPH.Child);
>
> When this query is executed by SQLite 3.16.2, the timer reports an
> execution time of 5.522 s. Adding an index on "Parent" and one on
> "Child" just makes things worse (6.381 s.)
>
> I find this figures quite high, so that I try an iterative technique,
> which is likely to be close to the execution strategy of the WITH
> statement (https://www.sqlite.org/lang_with.html). I translate it for
> the CLI shell as follows:
>
> update GRAPH set Level = 0 where Parent is null;
>
> update GRAPH set Level = 1
> where Parent in (select Child from GRAPH where Level = 0);
>
> update GRAPH set Level = 2
> where Parent in (select Child from GRAPH where Level = 1);
>
> update GRAPH set Level = 3
> where Parent in (select Child from GRAPH where Level = 2);
>
> update GRAPH set Level = 4
> where Parent in (select Child from GRAPH where Level = 3);
>
> update GRAPH set Level = 5
> where Parent in (select Child from GRAPH where Level = 4);
>
> update GRAPH set Level = 6
> where Parent in (select Child from GRAPH where Level = 5);
>
> For this script, I get an execution time of 0.015 s., i.e., nearly 370
> times less!
>
> Is there something wrong in my queries? Or is there an optimization
> trick for WITH queries by which one could approach the performance of
> the iterative version?
>
> The scripts are available here:
> https://www.dropbox.com/s/23t4ycftlk0doy1/GRAPH-performance.zip?dl=0
>
> Thanks for any advice
>
> Jean-Luc Hainaut
>
> _______________________________________________
> sqlite-users mailing list
> sqlite-users@mailinglists.sqlite.org
> http://mailinglists.sqlite.org/cgi-bin/mailman/listinfo/sqlite-users
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