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Simplified experimental changes to promote the use of co-routines. Less

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cruft than the coroutines-exp1 branch, but still does not work.  Checked in
as a work-in-progress.

FossilOrigin-Name: e2318a30bf6ad2aeb4c4cb29661bc24ff78eb51bf07decc4b8da1ecac0015ef0
This commit is contained in:
drh
2022-12-06 15:24:05 +00:00
parent d84f185f97
commit ad9ff1d5f2
6 changed files with 65 additions and 35 deletions
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74
src/select.c
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@@ -6854,6 +6854,52 @@ static int sameSrcAlias(SrcItem *p0, SrcList *pSrc){
return 0;
}
/*
** Return TRUE (non-zero) if the i-th entry in the pTabList SrcList can
** be implemented as a co-routine. The i-th entry is guaranteed to be
** a subquery.
**
** The subquery is implemented as a co-routine if all of the following are
** true:
**
** (1) Either of the following are true:
** (1a) The subquery must be the outer loop because it is either
** (i) the only term in the FROM clause, or because (ii) it
** is the left-most term and a CROSS JOIN or similar requires
** it to be the outer loop. subquery and there is nothing
** (1b) There is nothing that would prevent the subquery from
** being an outer loop and the SQLITE_PREPARE_SAFESQL flag
** is not set.
** (2) The subquery is not a CTE that should be materialized
** (3) The subquery is not part of a left operand for a RIGHT JOIN
** (4) The SQLITE_Coroutine optimization disable flag is not set
*/
static int fromClauseTermCanBeCoroutine(
Parse *pParse, /* Parsing context */
SrcList *pTabList, /* FROM clause */
int i /* Which term of the FROM clause */
){
SrcItem *pItem = &pTabList->a[i];
if( pItem->fg.isCte && pItem->u2.pCteUse->eM10d==M10d_Yes ) return 0;/* (2) */
if( pTabList->a[0].fg.jointype & JT_LTORJ ) return 0; /* (3) */
if( OptimizationDisabled(pParse->db, SQLITE_Coroutines) ) return 0; /* (4) */
if( i==0 ){
if( pTabList->nSrc==1 ) return 1; /* (1a-i) */
if( pTabList->a[1].fg.jointype & JT_CROSS ) return 1; /* (1a-ii) */
if( pParse->prepFlags & SQLITE_PREPARE_SAFEOPT ) return 0;
return 1;
}
if( pParse->prepFlags & SQLITE_PREPARE_SAFEOPT ) return 0;
while( 1 /*exit-by-break*/ ){
if( pItem->fg.jointype & (JT_OUTER|JT_CROSS) ) return 0;
if( i==0 ) break;
i--;
pItem--;
if( pItem->pSelect!=0 ) return 0;
}
return 1;
}
/*
** Generate code for the SELECT statement given in the p argument.
**
@@ -7241,35 +7287,19 @@ int sqlite3Select(
pParse->zAuthContext = pItem->zName;
/* Generate code to implement the subquery
**
** The subquery is implemented as a co-routine if all of the following are
** true:
**
** (1) the subquery is guaranteed to be the outer loop (so that
** it does not need to be computed more than once), and
** (2) the subquery is not a CTE that should be materialized
** (3) the subquery is not part of a left operand for a RIGHT JOIN
*/
if( i==0
&& (pTabList->nSrc==1
|| (pTabList->a[1].fg.jointype&(JT_OUTER|JT_CROSS))!=0) /* (1) */
&& (pItem->fg.isCte==0 || pItem->u2.pCteUse->eM10d!=M10d_Yes) /* (2) */
&& (pTabList->a[0].fg.jointype & JT_LTORJ)==0 /* (3) */
){
if( fromClauseTermCanBeCoroutine(pParse, pTabList, i) ){
/* Implement a co-routine that will return a single row of the result
** set on each invocation.
*/
int addrTop = sqlite3VdbeCurrentAddr(v)+1;
#ifdef SQLITE_ENABLE_STMT_SCANSTATUS
int addrExplain;
#endif
pItem->regReturn = ++pParse->nMem;
sqlite3VdbeAddOp3(v, OP_InitCoroutine, pItem->regReturn, 0, addrTop);
VdbeComment((v, "%!S", pItem));
pItem->addrFillSub = addrTop;
sqlite3SelectDestInit(&dest, SRT_Coroutine, pItem->regReturn);
ExplainQueryPlan2(addrExplain, (pParse, 1, "CO-ROUTINE %!S", pItem));
ExplainQueryPlan((pParse, 1, "CO-ROUTINE %!S", pItem));
sqlite3Select(pParse, pSub, &dest);
pItem->pTab->nRowLogEst = pSub->nSelectRow;
pItem->fg.viaCoroutine = 1;
@@ -7277,10 +7307,6 @@ int sqlite3Select(
sqlite3VdbeEndCoroutine(v, pItem->regReturn);
sqlite3VdbeJumpHere(v, addrTop-1);
sqlite3ClearTempRegCache(pParse);
/* For SQLITE_SCANSTAT_NCYCLE, all instructions from the
** OP_InitCoroutine coded above until this point are attributed to
** the CO-ROUTINE query element. */
sqlite3VdbeScanStatusRange(v, addrExplain, addrExplain-1, -1);
}else if( pItem->fg.isCte && pItem->u2.pCteUse->addrM9e>0 ){
/* This is a CTE for which materialization code has already been
** generated. Invoke the subroutine to compute the materialization,
@@ -7335,6 +7361,7 @@ int sqlite3Select(
if( onceAddr ) sqlite3VdbeJumpHere(v, onceAddr);
sqlite3VdbeAddOp2(v, OP_Return, pItem->regReturn, topAddr+1);
VdbeComment((v, "end %!S", pItem));
sqlite3VdbeScanStatusRange(v, addrExplain, addrExplain, -1);
sqlite3VdbeJumpHere(v, topAddr);
sqlite3ClearTempRegCache(pParse);
if( pItem->fg.isCte && pItem->fg.isCorrelated==0 ){
@@ -7344,9 +7371,6 @@ int sqlite3Select(
pCteUse->iCur = pItem->iCursor;
pCteUse->nRowEst = pSub->nSelectRow;
}
/* For SQLITE_SCANSTAT_NCYCLE, all instructions from the
** OP_Explain to here are attibuted to the MATERIALIZE element. */
sqlite3VdbeScanStatusRange(v, addrExplain, addrExplain, -1);
}
if( db->mallocFailed ) goto select_end;
pParse->nHeight -= sqlite3SelectExprHeight(p);