Snowflake DEA-C01 SnowPro Advanced Data Engineer Certification Online Training

Question #1

Streams cannot be created to query change data on which of the following objects? [Select All that Apply]

A . Standard tables, including shared tables.
B . Views, including secure views
C . Directory tables
D . Query Log Tables
E . External tables

Question #2

Tasks may optionally use table streams to provide a convenient way to continuously process new or changed data. A task can transform new or changed rows that a stream surfaces. Each time a task is scheduled to run, it can verify whether a stream contains change data for a table and either consume the change data or skip the current run if no change data exists.

Which System Function can be used by Data engineer to verify whether a stream contains changed data for a table?

A . SYSTEM$STREAM_HAS_CHANGE_DATA
B . SYSTEM$STREAM_CDC_DATA
C . SYSTEM$STREAM_HAS_DATA
D . SYSTEM$STREAM_DELTA_DATA

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Question #3

The Above example indicates that the SF_DATA table is not well-clustered for which of following valid reasons?

A . Zero (0) constant micro-partitions out of 1156 total micro-partitions.
B . High average of overlapping micro-partitions.
C . High average of overlap depth across micro-partitions.
D . Most of the micro-partitions are grouped at the lower-end of the histogram, with the majority of micro-partitions having an overlap depth between 64 and 128.
E . ALL of the above

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Question #4

Mark a Data Engineer, looking to implement streams on local views & want to use change tracking metadata for one of its Data Loading use case. Please select the incorrect understanding points of Mark with respect to usage of Streams on Views?

A . For streams on views, change tracking must be enabled explicitly for the view and underlying tables to add the hidden columns to these tables.
B . The CDC records returned when querying a stream rely on a combination of the offset stored in the stream and the change tracking metadata stored in the table.
C . Views with GROUP BY & LIMIT Clause are supported by Snowflake.
D . As an alternative to streams, Snowflake supports querying change tracking metadata for views using the CHANGES clause for SELECT statements.
E . Enabling change tracking adds a pair of hidden columns to the table and begins storing change tracking metadata. The values in these hidden CDC data columns provide the input for the stream metadata columns. The columns consume a small amount of storage.

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Correct Answer: C
C

Explanation:

A stream object records data manipulation language (DML) changes made to tables, including inserts, updates, and deletes, as well as metadata about each change, so that actions can be taken using the changed data. This process is referred to as change data capture (CDC). An individual table stream tracks the changes made to rows in a source table. A table stream (also referred to as simply a “stream”) makes a “change table” available of what changed, at the row level, between two transactional points of time in a table. This allows querying and consuming a sequence of change records in a transactional fashion.

Streams can be created to query change data on the following objects:

・ Standard tables, including shared tables.

・ Views, including secure views

・ Directory tables

・ External tables

When created, a stream logically takes an initial snapshot of every row in the source object (e.g. table, external table, or the underlying tables for a view) by initializing a point in time (called an off-set) as the current transactional version of the object. The change tracking system utilized by the stream then records information about the DML changes after this snapshot was taken. Change records provide the state of a row before and after the change. Change information mirrors the column structure of the tracked source object and includes additional metadata columns that describe each change event.

Note that a stream itself does not contain any table data. A stream only stores an offset for the source object and returns CDC records by leveraging the versioning history for the source object. When the first stream for a table is created, a pair of hidden columns are added to the source table and begin storing change tracking metadata. These columns consume a small amount of storage. The CDC records returned when querying a stream rely on a combination of the offset stored in the stream and the change tracking metadata stored in the table. Note that for streams on views, change tracking must be enabled explicitly for the view and underlying tables to add the hidden columns to these tables.

Streams on views support both local views and views shared using Snowflake Secure Data Sharing, including secure views. Currently, streams cannot track changes in materialized views.

Views with the following operations are not yet supported:

・ GROUP BY clauses

・ QUALIFY clauses

・ Subqueries not in the FROM clause

・ Correlated subqueries

・ LIMIT clauses

Change Tracking:

Change tracking must be enabled in the underlying tables.

Prior to creating a stream on a view, you must enable change tracking on the underlying tables for the view.

Set the CHANGE_TRACKING parameter when creating a view (using CREATE VIEW) or later (using ALTER VIEW).

As an alternative to streams, Snowflake supports querying change tracking metadata for tables or views using the CHANGES clause for SELECT statements. The CHANGES clause enables querying change tracking metadata between two points in time without having to create a stream with an explicit transactional offset.

Question #5

To advance the offset of a stream to the current table version without consuming the change data in a DML operation, which of the following operations can be done by Data Engineer? [Select 2]

A . using the CREATE OR REPLACE STREAM syntax, Recreate the STREAM
B . Insert the current change data into a temporary table. In the INSERT statement, query the stream but include a WHERE clause that filters out all of the change data (e.g. WHERE 0 = 1).
C . A stream advances the offset only when it is used in a DML transaction, so none of the options works without consuming the change data of table.
D . Delete the offset using STREAM properties SYSTEM$RESET_OFFSET( <stream_id> )

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Correct Answer: A, B
A, B

Explanation:

When created, a stream logically takes an initial snapshot of every row in the source object (e.g. table, external table, or the underlying tables for a view) by initializing a point in time (called an off-set) as the current transactional version of the object. The change tracking system utilized by the stream then records information about the DML changes after this snapshot was taken. Change records provide the state of a row before and after the change. Change information mirrors the column structure of the tracked source object and includes additional metadata columns that describe each change event.

Note that a stream itself does not contain any table data. A stream only stores an offset for the source object and returns CDC records by leveraging the versioning history for the source object.

A new table version is created whenever a transaction that includes one or more DML statements is committed to the table.

In the transaction history for a table, a stream offset is located between two table versions. Querying a stream returns the changes caused by transactions committed after the offset and at or before the current time.

Multiple queries can independently consume the same change data from a stream without changing the offset. A stream advances the offset only when it is used in a DML transaction. This behavior applies to both explicit and autocommit transactions. (By default, when a DML statement is executed, an autocommit transaction is implicitly started and the transaction is committed at the completion of the statement. This behavior is controlled with the AUTOCOMMIT parameter.) Querying a stream alone does not advance its offset, even within an explicit transaction; the stream contents must be consumed in a DML statement.

To advance the offset of a stream to the current table version without consuming the change data in a DML operation, complete either of the following actions:

・ Recreate the stream (using the CREATE OR REPLACE STREAM syntax).

Insert the current change data into a temporary table. In the INSERT statement, query the stream but include a WHERE clause that filters out all of the change data (e.g. WHERE 0 = 1).

Question #6

Data Engineer is performing below steps in sequence while working on Stream s1 created on table t1.

Step 1: Begin transaction.

Step 2: Query stream s1 on table t1.

Step 3: Update rows in table t1.

Step 4: Query stream s1.

Step 5: Commit transaction.

Step 6: Begin transaction.

Step 7: Query stream s1.

Mark the Incorrect Operational statements:

A . For Step 2, The stream returns the change data capture records between the current position to the Transaction 1 start time. If the stream is used in a DML statement, the stream is then locked to avoid changes by concurrent transactions.
B . For Step 4, Returns the CDC data records by streams with updated rows happened in the Step 3 because Streams works in Repeated committed mode in which statements see any changes made by previous statements executed within the same transaction, even though those changes are not yet committed.
C . For Step 5, If the stream was consumed in DML statements within the transaction, the stream position advances to the transaction start time.
D . For Step 7, Results do include table changes committed by Transaction 1.
E . if Transaction 2 had begun before Transaction 1 was committed, queries to the stream would have returned a snapshot of the stream from the position of the stream to the be-ginning time of Transaction 2 and would not see any changes committed by Transaction 1.

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Question #7

Streams record the differences between two offsets.

If a row is added and then updated in the cur-rent offset, what will be the value of METADATA$ISUPDATE Columns in this scenario?

A . TRUE
B . FALSE
C . UPDATE
D . INSERT

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Question #8

Mark the Incorrect Statements with respect to types of streams supported by Snowflake?

A . Standard streams cannot retrieve update data for geospatial data.
B . An append-only stream returns the appended rows only and therefore can be much more performant than a standard stream for extract, load, transform (ELT).
C . Insert-only Stream supported on external tables only.
D . An insert-only stream tracks row inserts & Delete ops only

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Question #9

Stuart, a Lead Data Engineer in MACRO Data Company created streams on set of External tables.

He has been asked to extend the data retention period of the stream for 90 days, which parameter he can utilize to enable this extension?

A . MAX_DATA_EXTENSION_TIME_IN_DAYS
B . DATA_RETENTION_TIME_IN_DAYS
C . DATA_EXTENSION_TIME_IN_DAYS
D . None of the above

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Question #9

Stuart, a Lead Data Engineer in MACRO Data Company created streams on set of External tables.

He has been asked to extend the data retention period of the stream for 90 days, which parameter he can utilize to enable this extension?

A . MAX_DATA_EXTENSION_TIME_IN_DAYS
B . DATA_RETENTION_TIME_IN_DAYS
C . DATA_EXTENSION_TIME_IN_DAYS
D . None of the above

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Snowflake DEA-C01 SnowPro Advanced Data Engineer Certification Online Training