DP-203 Design and implement data storage Practice Question
A retail company uses Azure Synapse Analytics dedicated SQL pool to store sales data. The data is loaded nightly from Azure Data Lake Storage Gen2 using PolyBase. Recently, the load process started failing with the error 'External table 'sales' is not accessible because the location does not exist or is used by another process.' You verify that the storage account, container, and file path are correct. The file is a CSV file named 'sales_20250301.csv' and it exists. Other files in the same container load successfully. What is the most likely cause of the error?
⚠ Common exam trap
It's easy for candidates to confuse file-locking errors with authentication or schema issues, but the specific wording 'used by another process' directly points to a concurrency/lock conflict rather than connectivity or data format problems.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The file is being written to or is locked by another process during the PolyBase read.
The error 'location does not exist or is used by another process' specifically indicates that the file is locked by another process. In Azure Data Lake Storage Gen2, when a file is being written or modified, it can be locked by the writing process (e.g., a data ingestion pipeline or another ETL job). PolyBase attempts to read the file while it is still being written, causing the error. Option D correctly identifies this concurrency issue.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The network connectivity between Synapse and the storage account is intermittent.
Why it's wrong here
Intermittent network issues would likely cause timeouts or different errors, not a 'location does not exist' error.
- ✗
The CSV file has an incorrect number of columns or contains a header row that mismatches the schema.
Why it's wrong here
Schema mismatch would cause a different error, such as 'column ordinal' or 'data type conversion' error.
- ✗
The storage account key used in the external data source has expired.
Why it's wrong here
If the key were expired, all loads would fail, not just one file.
- ✓
The file is being written to or is locked by another process during the PolyBase read.
Why this is correct
The error 'used by another process' indicates a file lock, typically because the file is still being written or another reader has an exclusive lock.
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