Google Cloud Dataflow SDK for Java, version 1.9.1
Class CompressedSource.CompressedReader<T>
- java.lang.Object
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- com.google.cloud.dataflow.sdk.io.Source.Reader<T>
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- com.google.cloud.dataflow.sdk.io.BoundedSource.BoundedReader<T>
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- com.google.cloud.dataflow.sdk.io.OffsetBasedSource.OffsetBasedReader<T>
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- com.google.cloud.dataflow.sdk.io.FileBasedSource.FileBasedReader<T>
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- com.google.cloud.dataflow.sdk.io.CompressedSource.CompressedReader<T>
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- Type Parameters:
T
- The type of records read from the source.
- All Implemented Interfaces:
- AutoCloseable
- Enclosing class:
- CompressedSource<T>
public static class CompressedSource.CompressedReader<T> extends FileBasedSource.FileBasedReader<T>
Reader for aCompressedSource
. Decompresses its input and uses a delegate reader to read elements from the decompressed input.
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Field Summary
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Fields inherited from class com.google.cloud.dataflow.sdk.io.BoundedSource.BoundedReader
SPLIT_POINTS_UNKNOWN
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Constructor Summary
Constructors Constructor and Description CompressedReader(CompressedSource<T> source, FileBasedSource.FileBasedReader<T> readerDelegate)
Create aCompressedReader
from aCompressedSource
and delegate reader.
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method and Description T
getCurrent()
Gets the current record from the delegate reader.protected long
getCurrentOffset()
Returns the starting offset of thecurrent record
, which has been read by the last successfulSource.Reader.start()
orSource.Reader.advance()
call.long
getSplitPointsConsumed()
Returns the total amount of parallelism in the consumed (returned and processed) range of this reader's currentBoundedSource
(as would be returned byBoundedSource.BoundedReader.getCurrentSource()
).long
getSplitPointsRemaining()
Returns the total amount of parallelism in the unprocessed part of this reader's currentBoundedSource
(as would be returned byBoundedSource.BoundedReader.getCurrentSource()
).protected boolean
isAtSplitPoint()
Returns true only for the first record; compressed sources cannot be split.protected boolean
readNextRecord()
Reads the next record via the delegate reader.protected void
startReading(ReadableByteChannel channel)
Creates a decompressing channel from the input channel and passes it to its delegate reader'sFileBasedReader#startReading(ReadableByteChannel)
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Methods inherited from class com.google.cloud.dataflow.sdk.io.FileBasedSource.FileBasedReader
advanceImpl, close, getCurrentSource, startImpl
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Methods inherited from class com.google.cloud.dataflow.sdk.io.OffsetBasedSource.OffsetBasedReader
advance, getFractionConsumed, isDone, isStarted, splitAtFraction, start
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Methods inherited from class com.google.cloud.dataflow.sdk.io.BoundedSource.BoundedReader
getCurrentTimestamp
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Constructor Detail
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CompressedReader
public CompressedReader(CompressedSource<T> source, FileBasedSource.FileBasedReader<T> readerDelegate)
Create aCompressedReader
from aCompressedSource
and delegate reader.
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Method Detail
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getCurrent
public T getCurrent() throws NoSuchElementException
Gets the current record from the delegate reader.- Specified by:
getCurrent
in classSource.Reader<T>
- Throws:
NoSuchElementException
- ifSource.Reader.start()
was never called, or if the lastSource.Reader.start()
orSource.Reader.advance()
returnedfalse
.
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getSplitPointsConsumed
public final long getSplitPointsConsumed()
Description copied from class:BoundedSource.BoundedReader
Returns the total amount of parallelism in the consumed (returned and processed) range of this reader's currentBoundedSource
(as would be returned byBoundedSource.BoundedReader.getCurrentSource()
). This corresponds to all split point records (seeRangeTracker
) returned by this reader, excluding the last split point returned if the reader is not finished.Consider the following examples: (1) An input that can be read in parallel down to the individual records, such as
CountingSource.upTo(long)
, is called "perfectly splittable". (2) a "block-compressed" file format such asAvroIO
, in which a block of records has to be read as a whole, but different blocks can be read in parallel. (3) An "unsplittable" input such as a cursor in a database.- Any
reader
that is unstarted (aka, has never had a call toSource.Reader.start()
) has a consumed parallelism of 0. This condition holds independent of whether the input is splittable. - Any
reader
that has only returned its first element (aka, has never had a call toSource.Reader.advance()
) has a consumed parallelism of 0: the first element is the current element and is still being processed. This condition holds independent of whether the input is splittable. - For an empty reader (in which the call to
Source.Reader.start()
returned false), the consumed parallelism is 0. This condition holds independent of whether the input is splittable. - For a non-empty, finished reader (in which the call to
Source.Reader.start()
returned true and a call toSource.Reader.advance()
has returned false), the value returned must be at least 1 and should equal the total parallelism in the source. - For example (1): After returning record #30 (starting at 1) out of 50 in a perfectly splittable 50-record input, this value should be 29. When finished, the consumed parallelism should be 50.
- For example (2): In a block-compressed value consisting of 5 blocks, the value should stay at 0 until the first record of the second block is returned; stay at 1 until the first record of the third block is returned, etc. Only once the end-of-file is reached then the fifth block has been consumed and the value should stay at 5.
- For example (3): For any non-empty unsplittable input, the consumed parallelism is 0
until the reader is finished (because the last call to
Source.Reader.advance()
returned false, at which point it becomes 1.
A reader that is implemented using a
RangeTracker
is encouraged to use the range tracker's ability to count split points to implement this method. SeeOffsetBasedSource.OffsetBasedReader
andOffsetRangeTracker
for an example.Defaults to
BoundedSource.BoundedReader.SPLIT_POINTS_UNKNOWN
. Any value less than 0 will be interpreted as unknown.Thread safety
See the javadoc onBoundedSource.BoundedReader
for information about thread safety.- Overrides:
getSplitPointsConsumed
in classOffsetBasedSource.OffsetBasedReader<T>
- See Also:
BoundedSource.BoundedReader.getSplitPointsRemaining()
- Any
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getSplitPointsRemaining
public final long getSplitPointsRemaining()
Description copied from class:BoundedSource.BoundedReader
Returns the total amount of parallelism in the unprocessed part of this reader's currentBoundedSource
(as would be returned byBoundedSource.BoundedReader.getCurrentSource()
). This corresponds to all unprocessed split point records (seeRangeTracker
), including the last split point returned, in the remainder part of the source.This function should be implemented only in addition to
BoundedSource.BoundedReader.getSplitPointsConsumed()
and only if an exact value can be returned.Consider the following examples: (1) An input that can be read in parallel down to the individual records, such as
CountingSource.upTo(long)
, is called "perfectly splittable". (2) a "block-compressed" file format such asAvroIO
, in which a block of records has to be read as a whole, but different blocks can be read in parallel. (3) An "unsplittable" input such as a cursor in a database.Assume for examples (1) and (2) that the number of records or blocks remaining is known:
- Any
reader
for which the last call toSource.Reader.start()
orSource.Reader.advance()
has returned true should should not return 0, because this reader itself represents parallelism at least 1. This condition holds independent of whether the input is splittable. - A finished reader (for which
Source.Reader.start()
orSource.Reader.advance()
) has returned false should return a value of 0. This condition holds independent of whether the input is splittable. - For example 1: After returning record #30 (starting at 1) out of 50 in a perfectly splittable 50-record input, this value should be 21 (20 remaining + 1 current) if the total number of records is known.
- For example 2: After returning a record in block 3 in a block-compressed file consisting of 5 blocks, this value should be 3 (since blocks 4 and 5 can be processed in parallel by new readers produced via dynamic work rebalancing, while the current reader continues processing block 3) if the total number of blocks is known.
- For example (3): a reader for any non-empty unsplittable input, should return 1 until it is finished, at which point it should return 0.
- For any reader: After returning the last split point in a file (e.g., the last record in example (1), the first record in the last block for example (2), or the first record in the file for example (3), this value should be 1: apart from the current task, no additional remainder can be split off.
Defaults to
BoundedSource.BoundedReader.SPLIT_POINTS_UNKNOWN
. Any value less than 0 will be interpreted as unknown.Thread safety
See the javadoc onBoundedSource.BoundedReader
for information about thread safety.- Overrides:
getSplitPointsRemaining
in classOffsetBasedSource.OffsetBasedReader<T>
- See Also:
BoundedSource.BoundedReader.getSplitPointsConsumed()
- Any
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isAtSplitPoint
protected final boolean isAtSplitPoint()
Returns true only for the first record; compressed sources cannot be split.- Overrides:
isAtSplitPoint
in classOffsetBasedSource.OffsetBasedReader<T>
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startReading
protected final void startReading(ReadableByteChannel channel) throws IOException
Creates a decompressing channel from the input channel and passes it to its delegate reader'sFileBasedReader#startReading(ReadableByteChannel)
.- Specified by:
startReading
in classFileBasedSource.FileBasedReader<T>
- Parameters:
channel
- a byte channel representing the file backing the reader.- Throws:
IOException
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readNextRecord
protected final boolean readNextRecord() throws IOException
Reads the next record via the delegate reader.- Specified by:
readNextRecord
in classFileBasedSource.FileBasedReader<T>
- Returns:
true
if a record was successfully read,false
if the end of the channel was reached before successfully reading a new record.- Throws:
IOException
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getCurrentOffset
protected final long getCurrentOffset() throws NoSuchElementException
Description copied from class:OffsetBasedSource.OffsetBasedReader
Returns the starting offset of thecurrent record
, which has been read by the last successfulSource.Reader.start()
orSource.Reader.advance()
call.If no such call has been made yet, the return value is unspecified.
See
RangeTracker
for description of offset semantics.- Specified by:
getCurrentOffset
in classOffsetBasedSource.OffsetBasedReader<T>
- Throws:
NoSuchElementException
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