org.apache.lucene.codecs.uniformsplit

## Class BlockWriter

- java.lang.Object
- - org.apache.lucene.codecs.uniformsplit.BlockWriter

- Direct Known Subclasses:
    STBlockWriter

      public class BlockWriter
      extends Object

  Writes blocks in the block file.

  According the Uniform Split technique, the writing combines three steps per block, and it is repeated for all the field blocks:

  1. Select the term with the shortest `minimal distinguishing prefix` (MDP) in the neighborhood of the `target block size` (+- `delta size`)
  2. The selected term becomes the first term of the next block, and its MDP is the next block key.
  3. The current block is written to the `block file`. And its block key is `added` to the `index dictionary`.

  This stateful `BlockWriter` is called repeatedly to `add` all the `BlockLine` terms of a field. Then `finishLastBlock(org.apache.lucene.codecs.uniformsplit.IndexDictionary.Builder)` is called. And then this `BlockWriter` can be reused to add the terms of another field.

  WARNING: This API is experimental and might change in incompatible ways in the next release.

- - ### Field Summary

    Fields
    Modifier and Type | Field and Description
    --- | ---
    `protected BlockEncoder` | `blockEncoder`
    `protected List<BlockLine>` | `blockLines`
    `protected ByteBuffersDataOutput` | `blockLinesWriteBuffer`
    `protected IndexOutput` | `blockOutput`
    `protected ByteBuffersDataOutput` | `blockWriteBuffer`
    `protected int` | `deltaNumLines`
    `protected FieldMetadata` | `fieldMetadata`
    `protected BytesRef` | `lastTerm`
    `protected BlockHeader` | `reusableBlockHeader`
    `protected BytesRef` | `scratchBytesRef`
    `protected int` | `targetNumBlockLines`
    `protected DeltaBaseTermStateSerializer` | `termStateSerializer`
    `protected ByteBuffersDataOutput` | `termStatesWriteBuffer`

  - ### Constructor Summary

    Constructors
    Modifier | Constructor and Description
    --- | ---
    `protected` | `BlockWriter(IndexOutput blockOutput, int targetNumBlockLines, int deltaNumLines, BlockEncoder blockEncoder)`

  - ### Method Summary

    All Methods Instance Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `protected void` | `addBlockKey(List<BlockLine> blockLines, IndexDictionary.Builder dictionaryBuilder)` Adds a new block key with its corresponding block file pointer to the `IndexDictionary.Builder` .
    `protected void` | `addLine(BytesRef term, BlockTermState blockTermState, IndexDictionary.Builder dictionaryBuilder)` Adds a new `BlockLine` term for the current field.
    `protected void` | `finishLastBlock(IndexDictionary.Builder dictionaryBuilder)` This method is called when there is no more term for the field.
    `protected void` | `splitAndWriteBlock(IndexDictionary.Builder dictionaryBuilder)` Defines the new block start according to `targetNumBlockLines` and `deltaNumLines`.
    `protected void` | `updateFieldMetadata(long blockStartFP)` updates the field metadata after all lines were written for the block.
    `protected void` | `writeBlock(List<BlockLine> blockLines, IndexDictionary.Builder dictionaryBuilder)` Writes a block and adds its block key to the dictionary builder.
    `protected void` | `writeBlockLine(boolean isIncrementalEncodingSeed, BlockLine line, BlockLine previousLine)`

    - ### Methods inherited from class java.lang.Object

      `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

- - ### Field Detail

    - #### targetNumBlockLines

          protected final int targetNumBlockLines

    - #### deltaNumLines

          protected final int deltaNumLines

    - #### blockLines

          protected final List<BlockLine> blockLines

    - #### blockOutput

          protected final IndexOutput blockOutput

    - #### blockLinesWriteBuffer

          protected final ByteBuffersDataOutput blockLinesWriteBuffer

    - #### termStatesWriteBuffer

          protected final ByteBuffersDataOutput termStatesWriteBuffer

    - #### termStateSerializer

          protected final DeltaBaseTermStateSerializer termStateSerializer

    - #### blockEncoder

          protected final BlockEncoder blockEncoder

    - #### blockWriteBuffer

          protected final ByteBuffersDataOutput blockWriteBuffer

    - #### fieldMetadata

          protected FieldMetadata fieldMetadata

    - #### lastTerm

          protected BytesRef lastTerm

    - #### reusableBlockHeader

          protected final BlockHeader reusableBlockHeader

    - #### scratchBytesRef

          protected BytesRef scratchBytesRef

  - ### Constructor Detail

    - #### BlockWriter

          protected BlockWriter(IndexOutput blockOutput,
                                int targetNumBlockLines,
                                int deltaNumLines,
                                BlockEncoder blockEncoder)

  - ### Method Detail

    - #### addLine

          protected void addLine(BytesRef term,
                                 BlockTermState blockTermState,
                                 IndexDictionary.Builder dictionaryBuilder)
                          throws IOException

      Adds a new `BlockLine` term for the current field.

      This method determines whether the new term is part of the current block, or if it is part of the next block. In the latter case, a new block is started (including one or more of the lastly added lines), the current block is written to the block file, and the current block key is added to the `IndexDictionary.Builder`.

      Parameters:
        `term` - The block line term. The `BytesRef` instance is used directly, the caller is responsible to make a deep copy if needed. This is required because we keep a list of block lines until we decide to write the current block, and each line must have a different term instance.
        `blockTermState` - Block line details.
        `dictionaryBuilder` - to which the block keys are added.
      Throws:
        `IOException`

    - #### finishLastBlock

          protected void finishLastBlock(IndexDictionary.Builder dictionaryBuilder)
                                  throws IOException

      This method is called when there is no more term for the field. It writes the remaining lines added with `addLine(org.apache.lucene.util.BytesRef, org.apache.lucene.codecs.BlockTermState, org.apache.lucene.codecs.uniformsplit.IndexDictionary.Builder)` as the last block of the field and resets this `BlockWriter` state. Then this `BlockWriter` can be used for another field.
      Throws:
        `IOException`

    - #### splitAndWriteBlock

          protected void splitAndWriteBlock(IndexDictionary.Builder dictionaryBuilder)
                                     throws IOException

      Defines the new block start according to `targetNumBlockLines` and `deltaNumLines`. The new block is started (including one or more of the lastly added lines), the current block is written to the block file, and the current block key is added to the `IndexDictionary.Builder`.
      Throws:
        `IOException`

    - #### writeBlock

          protected void writeBlock(List<BlockLine> blockLines,
                                    IndexDictionary.Builder dictionaryBuilder)
                             throws IOException

      Writes a block and adds its block key to the dictionary builder.
      Throws:
        `IOException`

    - #### updateFieldMetadata

          protected void updateFieldMetadata(long blockStartFP)

      updates the field metadata after all lines were written for the block.

    - #### writeBlockLine

          protected void writeBlockLine(boolean isIncrementalEncodingSeed,
                                        BlockLine line,
                                        BlockLine previousLine)
                                 throws IOException

      Throws:
        `IOException`

    - #### addBlockKey

          protected void addBlockKey(List<BlockLine> blockLines,
                                     IndexDictionary.Builder dictionaryBuilder)

      Adds a new block key with its corresponding block file pointer to the `IndexDictionary.Builder` . The block key is the MDP (see `TermBytes`) of the block first term.

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