github.com/m3db/m3@v1.5.0/src/dbnode/persist/fs/msgpack/summary_token.go (about)

     1  // Copyright (c) 2017 Uber Technologies, Inc
     2  //
     3  // Permission is hereby granted, free of charge, to any person obtaining a copy
     4  // of this software and associated documentation files (the "Software"), to deal
     5  // in the Software without restriction, including without limitation the rights
     6  // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
     7  // copies of the Software, and to permit persons to whom the Software is
     8  // furnished to do so, subject to the following conditions:
     9  //
    10  // The above copyright notice and this permission notice shall be included in
    11  // all copies or substantial portions of the Software
    12  //
    13  // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
    14  // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
    15  // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
    16  // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
    17  // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
    18  // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
    19  // THE SOFTWARE
    20  
    21  package msgpack
    22  
    23  import (
    24  	"gopkg.in/vmihailenco/msgpack.v2"
    25  )
    26  
    27  // IndexSummaryToken can be used, along with the summaries file buffer, to
    28  // quickly retrieve the ID or index file offset of an index summary entry.
    29  // It's structured such that the ID and Index file offset can be retrieved
    30  // quickly, while only requiring 64-bits of memory per entry.
    31  type IndexSummaryToken struct {
    32  	// The offset into the underlying byte array at which the bytes for the ID begin
    33  	idStartOffset uint32
    34  	// The length of the bytes for the ID
    35  	idLength uint32
    36  }
    37  
    38  // ID returns the ID that the metadata corresponds to
    39  func (m IndexSummaryToken) ID(buf []byte) []byte {
    40  	idStart := m.idStartOffset
    41  	idEnd := idStart + m.idLength
    42  	return buf[idStart:idEnd]
    43  }
    44  
    45  // IndexOffset returns the offset in the index file for the series that the
    46  // metadata corresponds to. The buf, stream, and decoder arguments are passed in
    47  // so that the IndexSummaryToken struct can be kept small, as well as
    48  // so that the caller can have control over re-use and allocations.
    49  func (m IndexSummaryToken) IndexOffset(
    50  	buf []byte, stream ByteDecoderStream, msgpackDecoder *msgpack.Decoder) (int64, error) {
    51  	idStart := m.idStartOffset
    52  	idEnd := idStart + m.idLength
    53  	indexOffsetStart := int(idEnd)
    54  
    55  	stream.Reset(buf[indexOffsetStart:])
    56  	msgpackDecoder.Reset(stream)
    57  	indexOffset, err := msgpackDecoder.DecodeInt64()
    58  	// Should never happen, either something is really wrong with the code or
    59  	// the file on disk was corrupted
    60  	if err != nil {
    61  		return -1, err
    62  	}
    63  	return indexOffset, nil
    64  }
    65  
    66  // NewIndexSummaryToken returns a new IndexSummaryToken
    67  func NewIndexSummaryToken(idStartOffset, idLength uint32) IndexSummaryToken {
    68  	return IndexSummaryToken{
    69  		idStartOffset: idStartOffset,
    70  		idLength:      idLength,
    71  	}
    72  }