I patched my SQlite 3.24 code to include the fix from the ticket
< if( rc==SQLITE_OK && (mBest = (pNew->prereq & ~mPrereq))!=0 ){
---
> // from SQLite bugfix
> if( rc==SQLITE_OK && ((mBest = (pNew->prereq & ~mPrereq))!=0 || bIn) ){
and changed the xBestIndex return value to be lower if the equality constraint
from IN is not usable
The generated code as reported is invalid (instruction 16 with the init of R6
is not shown)
explain select lsn from atx_txlog where period_no between 7300 and 7313 and
event_Type in (140001,180001);
addr opcode p1 p2 p3 p4 p5 comment
---- ------------- ---- ---- ---- ------------- -- -------------
0 Init 0 16 0 00 Start at 16
1 VOpen 0 0 0 vtab:B90B50 00
2 Explain 2 0 0 SCAN TABLE atx_txlog VIRTUAL TABLE INDEX
1:
00
3 Integer 7300 3 0 00 r[3]=7300
4 Integer 7313 4 0 00 r[4]=7313
5 Integer 1 1 0 00 r[1]=1
6 Integer 2 2 0 00 r[2]=2
7 VFilter 0 15 1
00 iplan=r[1] zplan='
'
8 Noop 0 0 0 00 begin IN expr
9 VColumn 0 15 5 00 r[5]=vcolumn(15);
atx_txlog.event_type
10 Eq 5 12 6 (BINARY) 43 if r[6]==r[5] goto
12
11 Ne 5 14 7 (BINARY) 53 if r[7]!=r[5] goto
14; end IN expr
12 VColumn 0 21 8 00 r[8]=vcolumn(21);
atx_txlog.lsn
13 ResultRow 8 1 0 00 output=r[8]
14 VNext 0 8 0 00
15 Halt 0 0 0 00
17 Integer 180001 7 0 00 r[7]=180001
18 Goto 0 1 0 00
-----Ursprüngliche Nachricht-----
Von: sqlite-users [mailto:[email protected]] Im
Auftrag von Dan Kennedy
Gesendet: Freitag, 29. März 2019 14:30
An: [email protected]
Betreff: [EXTERNAL] Re: [sqlite] Query Regression IN and Virtual Tables
On 29/3/62 14:32, Hick Gunter wrote:
> When upgrading from 3.7.14.1 to 3.24 I noticed the following problem
>
> Given a virtual table like
>
> CREATE VIRTUAL TABLE vt ( key1 INTEGER, key2 INTEGER, key3 INTEGER,
> attr1 INTEGER,...);
>
> whose xBestIndex function simulates (in unsupported syntax)
>
> CREATE VIRTUAL INDEX vt_key ON vt (key1, key2, key3);
>
> but also handles simple comparisons internally, the query
>
> SELECT * FROM vt WHERE key1 = <val1> AND key2 BETWEEN <val2> AND
> <val3> AND attr1 IN (<list>);
Thanks for reporting this.
What is supposed to happen in this scenario is that xBestIndex() is invoked
once with all 4 constraints marked as usable. The IN(...) is represented as an
SQLITE_INDEX_CONSTRAINT_EQ constraint. If the
xBestIndex() implementation elects to use the IN(...) operator, then
xBestIndex() is invoked a second time, this time with the IN(...) marked as not
usable. SQLite evaluates both plans, considering the cost estimates provided by
the virtual table implementation and its own estimate of the cardinality of the
IN(...) operator. And chooses the most efficient plan overall.
There was a bug preventing the second call to xBestIndex() from being made in
some circumstances - including for your query. Now fixed here:
https://sqlite.org/src/info/f5752517f590b37b
So if you upgrade to trunk, or else apply the patch linked above to 3.27.2, and
the virtual table implementation provides relatively accurate cost estimates,
SQLite should make an intelligent decision about which plan to use.
Dan.
>
> SQLite 3.7.14.1 asks for (key1,'='), (key2,'>='), (key2,'<=') and
> xBestIndex accepts all 3 constraints yielding query plan
>
> - materialize IN <list> as anonymous ephemeral table
> - search vt using index 1 (key1 = ? AND key2 >= ? AND key2 <= ?)
> - retrieve column attr1
> - search anonymous ephemeral table
>
> i.e. perform a single partial table scan on vt and check attr1
>
>
> SQLite3.24 asks for ...,(attr1,'=') and xBestIndex accepts all 4
> constraints yielding
>
> - materialize IN (<list>) as anonymous ephemeral table
> - scan anonymous ephemeral table
> - search vt using index 1 (key1 = ? AND key2 >= ? AND key2 <= ? AND
> attr1 = ?)
>
> i.e. perform a partial table scan of vt FOR EACH attr1, which is
> slower by the cardinality of the IN list
>
> Fortunately, CTEs come to the rescue:
>
> WITH attrs (attr1) AS (VALUES <(list)>) SELECT * FROM vt CROSS JOIN
> attrs a ON (a.attr1 = vt.attr1) WHERE key1 = <val1> AND key2 BETWEEN
> <val2> AND <val3>
>
> This prevents SQLite 3.24 from adding the last constraint, yielding
>
> - materialize IN (<(list)>) as epehemeral table attrs
> - search vt using index 1 (key1 = ? AND key2 >= ? AND key2 <= ?)
> - retrieve column attr1
> - scan ephemeral table attrs
>
> The only issue is that the previously generated ephemeral table was
> implemented as a covering index (allowing the sequence IfNull,
> Affinity, NotFound) whereas the named ephemeral table is implemented
> as a table (requiring a full table scan of the ephemeral table, even
> though at most 1 row can match)
>
> Optimisation opportunity:
>
> 32 Rewind 1 40 0 00
> 33 Column 1 0 10 00
> r[10]=events.event_type
> 34 VColumn 0 15 11 00
> r[11]=vcolumn(15); atx_txlog.event_type
> 35 Ne 11 38 10 (BINARY) 53 if r[10]!=r[11]
> goto 38
> 36 VColumn 0 6 12 00
> r[12]=vcolumn(6); atx_txlog.sync_offset
> 37 ResultRow 12 1 0 00 output=r[12]
> 38 Next 1 33 0 01
>
> Could IMHO be rewritten as
>
> 32 VColumn 0 15 11 00
> r[11]=vcolumn(15); atx_txlog.event_type
> 33 Rewind 1 40 0 00
> 34 Column 1 0 10 00
> r[10]=events.event_type
> 35 Ne 11 38 10 (BINARY) 53 if r[10]!=r[11]
> goto 38
> 36 VColumn 0 6 12 00
> r[12]=vcolumn(6); atx_txlog.sync_offset
> 37 ResultRow 12 1 0 00 output=r[12]
> 38 Next 1 33 0 01
>
>
> ___________________________________________
> Gunter Hick | Software Engineer | Scientific Games International
> GmbH | Klitschgasse 2-4, A-1130 Vienna | FN 157284 a, HG Wien, DVR:
> 0430013 | (O) +43 1 80100 - 0
>
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> [email protected]
> http://mailinglists.sqlite.org/cgi-bin/mailman/listinfo/sqlite-users
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Klitschgasse 2-4, A-1130 Vienna | FN 157284 a, HG Wien, DVR: 0430013 | (O) +43
1 80100 - 0
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