Podcast
Questions and Answers
What does a 'readstream' do differently than a standard 'read'?
What does a 'readstream' do differently than a standard 'read'?
- ignores deleted data
- Reads data from a single file
- Allows for real-time data processing (correct)
- Streams data from multiple tables
What type of DataFrame is returned by the 'readstream' function?
What type of DataFrame is returned by the 'readstream' function?
- Standard DataFrame
- Streaming DataFrame (correct)
- Real-Time DataFrame
- Delta DataFrame
What is the purpose of the 'load' function?
What is the purpose of the 'load' function?
- To save data to a file
- To load data from a file (correct)
- To read data from a source
- To stream data from a table
What is similar between a Streaming DataFrame and a standard DataFrame?
What is similar between a Streaming DataFrame and a standard DataFrame?
What is unique about the 'readstream' function compared to a standard 'read' function?
What is unique about the 'readstream' function compared to a standard 'read' function?
What is the purpose of the 'DESCRIBE HISTORY' query?
What is the purpose of the 'DESCRIBE HISTORY' query?
What is the type of source in the 'sources' section?
What is the type of source in the 'sources' section?
What type of sequence of data is a streaming DataFrame?
What type of sequence of data is a streaming DataFrame?
Why can't we perform a count() operation on a streaming DataFrame?
Why can't we perform a count() operation on a streaming DataFrame?
What is the purpose of adding a 'RecordStreamTime' column to the streaming DataFrame?
What is the purpose of adding a 'RecordStreamTime' column to the streaming DataFrame?
What is the purpose of selecting columns in the streaming DataFrame?
What is the purpose of selecting columns in the streaming DataFrame?
Why can't we perform a sort() operation on a streaming DataFrame?
Why can't we perform a sort() operation on a streaming DataFrame?
What is the purpose of the target location in writing the stream to an output table?
What is the purpose of the target location in writing the stream to an output table?
What is the purpose of the checkpoint location in writing the stream to an output table?
What is the purpose of the checkpoint location in writing the stream to an output table?
What happens when we write the stream to an output table?
What happens when we write the stream to an output table?
What is the default value for maxBytesPerTrigger?
What is the default value for maxBytesPerTrigger?
What happens when you use Trigger.Once?
What happens when you use Trigger.Once?
What is the purpose of the rate limit options?
What is the purpose of the rate limit options?
What does the ignoreDeletes option do?
What does the ignoreDeletes option do?
What is the effect of the ignoreChanges option?
What is the effect of the ignoreChanges option?
What is the purpose of controlling micro-batch size?
What is the purpose of controlling micro-batch size?
How can you control rate limits in a streaming query?
How can you control rate limits in a streaming query?
What is the effect of the readChangeFeed option?
What is the effect of the readChangeFeed option?
What is the purpose of the checkpoint file in a streaming query?
What is the purpose of the checkpoint file in a streaming query?
What happens if a trigger is not specified in a streaming query?
What happens if a trigger is not specified in a streaming query?
What information does the checkpoint file maintain about the transaction log entries?
What information does the checkpoint file maintain about the transaction log entries?
What is displayed in the streaming dashboard?
What is displayed in the streaming dashboard?
What is the purpose of the query progress log (QPL)?
What is the purpose of the query progress log (QPL)?
How many tabs are displayed in the streaming dashboard?
How many tabs are displayed in the streaming dashboard?
Flashcards
Streaming Query
Streaming Query
A query that reads data continuously from a source table, using readstream, enabling real-time processing.
readstream function
readstream function
A function used to read data from a source table in streaming mode, returning a streaming DataFrame.
Streaming DataFrame
Streaming DataFrame
A DataFrame designed for continuous data processing; unbounded and incompatible with operations like count() or sort().
RecordStreamTime
RecordStreamTime
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withColumn method
withColumn method
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select function
select function
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writeStream function
writeStream function
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Checkpoint Location
Checkpoint Location
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Query Progress Log (QPL)
Query Progress Log (QPL)
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Trigger Options
Trigger Options
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CDF Stream
CDF Stream
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Study Notes
Streaming Queries
- A streaming query is created by reading a stream from a source table using
readstreaminstead ofread - The
readstreamfunction is similar to a standard Delta table read, but returns a streaming DataFrame - A streaming DataFrame is similar to a standard Spark DataFrame, but is unbounded and cannot be used with certain operations like
count()orsort()
Adding a Timestamp Column
- A
RecordStreamTimecolumn can be added to the streaming DataFrame usingwithColumnandcurrent_timestamp() - This column captures the timestamp when each record is read from the source table
Selecting Columns
- The
selectfunction is used to select specific columns from the streaming DataFrame - The
select_columnslist specifies the columns to be selected
Writing to an Output Table
- The streaming DataFrame is written to an output table using
writeStream - A target location and checkpoint location are specified
- The checkpoint file maintains metadata and state of the streaming query, ensuring fault tolerance and enabling query recovery in case of failure
Query Progress Log
- When the streaming query is started, a query progress log (QPL) is displayed
- The QPL provides execution details on each micro-batch and is used to display a streaming dashboard in the notebook cell
- The dashboard provides metrics, statistics, and insights about the stream application's performance, throughput, and latency
Trigger Options
- Trigger options can be used to control the rate at which data is processed in each micro-batch
- Options include
maxBytesPerTrigger,ignoreDeletes, andignoreChanges - These options can be used to control rate limits and avoid overloading processing resources
Reading a CDF Stream
- A CDF (Change Data Feed) stream can be read using
readstreamwithreadChangeFeedoption - This allows for capturing changes made to the source table, such as inserts, updates, and deletes
- Rate limit options and ignore deletes can be specified to control the processing of the stream
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