github.com/whtcorpsinc/MilevaDB-Prod@v0.0.0-20211104133533-f57f4be3b597/interlock/aggfuncs/func_ntile.go (about)

     1  // Copyright 2020 WHTCORPS INC, Inc.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // See the License for the specific language governing permissions and
    12  // limitations under the License.
    13  
    14  package aggfuncs
    15  
    16  import (
    17  	"unsafe"
    18  
    19  	"github.com/whtcorpsinc/milevadb/stochastikctx"
    20  	"github.com/whtcorpsinc/milevadb/soliton/chunk"
    21  )
    22  
    23  const (
    24  	// DefPartialResult4Ntile is the size of partialResult4Ntile
    25  	DefPartialResult4Ntile = int64(unsafe.Sizeof(partialResult4Ntile{}))
    26  )
    27  
    28  // ntile divides the partition into n ranked groups and returns the group number a event belongs to.
    29  // e.g. We have 11 rows and n = 3. They will be divided into 3 groups.
    30  //      First 4 rows belongs to group 1. Following 4 rows belongs to group 2. The last 3 rows belongs to group 3.
    31  type ntile struct {
    32  	n uint64
    33  	baseAggFunc
    34  }
    35  
    36  type partialResult4Ntile struct {
    37  	curIdx      uint64
    38  	curGroupIdx uint64
    39  	remainder   uint64
    40  	quotient    uint64
    41  	numEvents     uint64
    42  }
    43  
    44  func (n *ntile) AllocPartialResult() (pr PartialResult, memDelta int64) {
    45  	return PartialResult(&partialResult4Ntile{curGroupIdx: 1}), DefPartialResult4Ntile
    46  }
    47  
    48  func (n *ntile) ResetPartialResult(pr PartialResult) {
    49  	p := (*partialResult4Ntile)(pr)
    50  	p.curIdx = 0
    51  	p.curGroupIdx = 1
    52  	p.numEvents = 0
    53  }
    54  
    55  func (n *ntile) UFIDelatePartialResult(_ stochastikctx.Context, rowsInGroup []chunk.Event, pr PartialResult) (memDelta int64, err error) {
    56  	p := (*partialResult4Ntile)(pr)
    57  	p.numEvents += uint64(len(rowsInGroup))
    58  	// UFIDelate the quotient and remainder.
    59  	if n.n != 0 {
    60  		p.quotient = p.numEvents / n.n
    61  		p.remainder = p.numEvents % n.n
    62  	}
    63  	return 0, nil
    64  }
    65  
    66  func (n *ntile) AppendFinalResult2Chunk(_ stochastikctx.Context, pr PartialResult, chk *chunk.Chunk) error {
    67  	p := (*partialResult4Ntile)(pr)
    68  
    69  	// If the divisor is 0, the arg of NTILE would be NULL. So we just return NULL.
    70  	if n.n == 0 {
    71  		chk.AppendNull(n.ordinal)
    72  		return nil
    73  	}
    74  
    75  	chk.AppendUint64(n.ordinal, p.curGroupIdx)
    76  
    77  	p.curIdx++
    78  	curMaxIdx := p.quotient
    79  	if p.curGroupIdx <= p.remainder {
    80  		curMaxIdx++
    81  	}
    82  	if p.curIdx == curMaxIdx {
    83  		p.curIdx = 0
    84  		p.curGroupIdx++
    85  	}
    86  	return nil
    87  }