greenplumn CXformSplitLimit 源码
greenplumn CXformSplitLimit 代码
文件路径:/src/backend/gporca/libgpopt/src/xforms/CXformSplitLimit.cpp
//---------------------------------------------------------------------------
// Greenplum Database
// Copyright (C) 2012 EMC Corp.
//
// @filename:
// CXformSplitLimit.cpp
//
// @doc:
// Implementation of the splitting of limit
//---------------------------------------------------------------------------
#include "gpopt/xforms/CXformSplitLimit.h"
#include "gpos/base.h"
#include "gpopt/base/CUtils.h"
#include "gpopt/operators/CExpressionHandle.h"
#include "gpopt/operators/CLogicalLimit.h"
#include "gpopt/operators/CPatternLeaf.h"
using namespace gpmd;
using namespace gpopt;
//---------------------------------------------------------------------------
// @function:
// CXformSplitLimit::CXformSplitLimit
//
// @doc:
// Ctor
//
//---------------------------------------------------------------------------
CXformSplitLimit::CXformSplitLimit(CMemoryPool *mp)
: CXformExploration(
// pattern
GPOS_NEW(mp) CExpression(
mp, GPOS_NEW(mp) CLogicalLimit(mp),
GPOS_NEW(mp) CExpression(
mp, GPOS_NEW(mp) CPatternLeaf(mp)), // relational child
GPOS_NEW(mp) CExpression(mp, GPOS_NEW(mp) CPatternLeaf(
mp)), // scalar child for offset
GPOS_NEW(mp) CExpression(
mp, GPOS_NEW(mp)
CPatternLeaf(mp)) // scalar child for number of rows
))
{
}
//---------------------------------------------------------------------------
// @function:
// CXformSplitLimit::Exfp
//
// @doc:
// Compute xform promise for a given expression handle;
//
//---------------------------------------------------------------------------
CXform::EXformPromise
CXformSplitLimit::Exfp(CExpressionHandle &exprhdl) const
{
if (0 < exprhdl.DeriveOuterReferences()->Size())
{
return CXform::ExfpNone;
}
CLogicalLimit *popLimit = CLogicalLimit::PopConvert(exprhdl.Pop());
if (!popLimit->FGlobal() || !popLimit->FHasCount())
{
return CXform::ExfpNone;
}
return CXform::ExfpHigh;
}
//---------------------------------------------------------------------------
// @function:
// CXformSplitLimit::Transform
//
// @doc:
// Actual transformation to expand a global limit into a pair of
// local and global limit
//
//---------------------------------------------------------------------------
void
CXformSplitLimit::Transform(CXformContext *pxfctxt, CXformResult *pxfres,
CExpression *pexpr) const
{
GPOS_ASSERT(nullptr != pxfctxt);
GPOS_ASSERT(nullptr != pxfres);
GPOS_ASSERT(FPromising(pxfctxt->Pmp(), this, pexpr));
GPOS_ASSERT(FCheckPattern(pexpr));
CMemoryPool *mp = pxfctxt->Pmp();
// extract components
CLogicalLimit *popLimit = CLogicalLimit::PopConvert(pexpr->Pop());
CExpression *pexprRelational = (*pexpr)[0];
CExpression *pexprScalarStart = (*pexpr)[1];
CExpression *pexprScalarRows = (*pexpr)[2];
COrderSpec *pos = popLimit->Pos();
// TODO: , Feb 20, 2012, we currently only split limit with offset 0.
if (!CUtils::FHasZeroOffset(pexpr) ||
0 < pexprRelational->DeriveOuterReferences()->Size())
{
return;
}
// addref all components
pexprRelational->AddRef();
// assemble local limit operator
CExpression *pexprLimitLocal =
PexprLimit(mp, pexprRelational, pexprScalarStart, pexprScalarRows, pos,
false, // fGlobal
popLimit->FHasCount(), popLimit->IsTopLimitUnderDMLorCTAS());
// assemble global limit operator
CExpression *pexprLimitGlobal =
PexprLimit(mp, pexprLimitLocal, pexprScalarStart, pexprScalarRows, pos,
true, // fGlobal
popLimit->FHasCount(), popLimit->IsTopLimitUnderDMLorCTAS());
pxfres->Add(pexprLimitGlobal);
}
//---------------------------------------------------------------------------
// @function:
// CXformSplitLimit::PexprLimit
//
// @doc:
// Generate a limit operator
//
//---------------------------------------------------------------------------
CExpression *
CXformSplitLimit::PexprLimit(CMemoryPool *mp, CExpression *pexprRelational,
CExpression *pexprScalarStart,
CExpression *pexprScalarRows, COrderSpec *pos,
BOOL fGlobal, BOOL fHasCount,
BOOL fTopLimitUnderDML)
{
pexprScalarStart->AddRef();
pexprScalarRows->AddRef();
pos->AddRef();
// assemble global limit operator
CExpression *pexprLimit = GPOS_NEW(mp) CExpression(
mp,
GPOS_NEW(mp)
CLogicalLimit(mp, pos, fGlobal, fHasCount, fTopLimitUnderDML),
pexprRelational, pexprScalarStart, pexprScalarRows);
return pexprLimit;
}
// EOF
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