While this consistency guarantee under data change is weaker than that of reading Delta tables with Spark, it is still stronger than formats like Parquet as they do not provide partition-level consistency.ĭepending on what storage system you are using for Delta tables, it is possible to get incorrect results when Redshift Spectrum concurrently queries the manifest while the manifest files are being rewritten. Furthermore, since all manifests of all partitions cannot be updated together, concurrent attempts to generate manifests can lead to different partitions having manifests of different versions. This means that each partition is updated atomically, and Redshift Spectrum will see a consistent view of each partition but not a consistent view across partitions. Partitioned tables: A manifest file is partitioned in the same Hive-partitioning-style directory structure as the original Delta table.
#REDSHIFT MATERIALIZED VIEW LIMITATIONS FULL#
In this case Redshift Spectrum will see full table snapshot consistency. Unpartitioned tables: All the files names are written in one manifest file which is updated atomically. However, the granularity of the consistency guarantees depends on whether or not the table is partitioned. Therefore, Redshift Spectrum will always see a consistent view of the data files it will see all of the old version files or all of the new version files. Whenever Delta Lake generates updated manifests, it atomically overwrites existing manifest files. In addition, if your table is partitioned, then you must add any new partitions or remove deleted partitions by following the same process as described in the preceding step. Hence, if concurrent writes are expected and you want to avoid stale manifests, you should consider explicitly updating the manifest after the expected write operations have completed. With such unordered writes, the manifest files are not guaranteed to point to the latest version of the table after the write operations complete. For example, if automatic mode is enabled, concurrent write operations lead to concurrent overwrites to the manifest files.
#REDSHIFT MATERIALIZED VIEW LIMITATIONS UPDATE#
Whether to update automatically or explicitly depends on the concurrent nature of write operations on the Delta table and the desired data consistency. Therefore, you should explicitly run GENERATE to update manifests for the entire table immediately after enabling automatic mode. However, this also means that if the manifests in other partitions are stale, enabling automatic mode will not automatically fix it.
This incremental update ensures that the overhead of manifest generation is low for write operations.
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