On 5/4/62 16:44, Hick Gunter wrote:
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)
So, after applying the patch to 3.24 you executed the EXPLAIN statement shown below in the shell tool and it mysteriously omitted instruction 16 from the output?
Are there any other problems? Does the SQL statement return the correct results if you execute it without the EXPLAIN?
Dan.
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 May be privileged. May be confidential. Please delete if not the addressee. _______________________________________________ sqlite-users mailing list [email protected] http://mailinglists.sqlite.org/cgi-bin/mailman/listinfo/sqlite-users_______________________________________________ sqlite-users mailing list [email protected] http://mailinglists.sqlite.org/cgi-bin/mailman/listinfo/sqlite-users ___________________________________________ 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 May be privileged. May be confidential. Please delete if not the addressee. _______________________________________________ sqlite-users mailing list [email protected] http://mailinglists.sqlite.org/cgi-bin/mailman/listinfo/sqlite-users
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