greenplumn CXformSplitLimit 源码
greenplumn CXformSplitLimit 代码
文件路径：/src/backend/gporca/libgpopt/include/gpopt/xforms/CXformSplitLimit.h
//---------------------------------------------------------------------------
// Greenplum Database
// Copyright (C) 2012 EMC Corp.
//
// @filename:
// CXformSplitLimit.h
//
// @doc:
// Split a global limit into pair of local and global limit
//---------------------------------------------------------------------------
#ifndef GPOPT_CXformSplitLimit_H
#define GPOPT_CXformSplitLimit_H
#include "gpos/base.h"
#include "gpopt/xforms/CXformExploration.h"
namespace gpopt
{
using namespace gpos;
//---------------------------------------------------------------------------
// @class:
// CXformSplitLimit
//
// @doc:
// Split a global limit into pair of local and global limit
//
//---------------------------------------------------------------------------
class CXformSplitLimit : public CXformExploration
{
private:
// helper function for creating a limit expression
static CExpression *PexprLimit(
CMemoryPool *mp, // memory pool
CExpression *pexprRelational, // relational child
CExpression *pexprScalarStart, // limit offset
CExpression *pexprScalarRows, // limit count
COrderSpec *pos, // ordering specification
BOOL fGlobal, // is it a local or global limit
BOOL fHasCount, // does limit specify a number of rows
BOOL fTopLimitUnderDML);
public:
CXformSplitLimit(const CXformSplitLimit &) = delete;
// ctor
explicit CXformSplitLimit(CMemoryPool *mp);
// dtor
~CXformSplitLimit() override = default;
// ident accessors
EXformId
Exfid() const override
{
return ExfSplitLimit;
}
// return a string for xform name
const CHAR *
SzId() const override
{
return "CXformSplitLimit";
}
// Compatibility function for splitting limit
BOOL
FCompatible(CXform::EXformId exfid) override
{
return (CXform::ExfSplitLimit != exfid);
}
// compute xform promise for a given expression handle
EXformPromise Exfp(CExpressionHandle &exprhdl) const override;
// actual transform
void Transform(CXformContext *pxfctxt, CXformResult *pxfres,
CExpression *pexpr) const override;
}; // class CXformSplitLimit
} // namespace gpopt
#endif // !GPOPT_CXformSplitLimit_H
// EOF
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