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https://issues.apache.org/jira/browse/IMPALA-12487?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Work on IMPALA-12487 started by Sai Hemanth Gantasala.
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> Skip reloading file metadata for ALTER_TABLE events with trivial changes in
> StorageDescriptor
> ---------------------------------------------------------------------------------------------
>
> Key: IMPALA-12487
> URL: https://issues.apache.org/jira/browse/IMPALA-12487
> Project: IMPALA
> Issue Type: Improvement
> Reporter: Quanlong Huang
> Assignee: Sai Hemanth Gantasala
> Priority: Critical
> Attachments: ALTER_TABLE_event_with_SD_changes.png
>
>
> IMPALA-11534 skips reloading file metadata for some trivial ALTER_TABLE
> events. However, ALTER_TABLE events that have trivial changes in
> StorageDescriptor are not handled in IMPALA-11534. Some of them can skip
> reloading file metadata. The thrift defination of StorageDescriptor (not all
> of the fields are related to file metadata):
> {code:java}
> // this object holds all the information about physical storage of the data
> belonging to a table
> struct StorageDescriptor {
> 1: list<FieldSchema> cols, // required (refer to types defined above)
> 2: string location, // defaults to <warehouse loc>/<db
> loc>/tablename
> 3: string inputFormat, // SequenceFileInputFormat (binary) or
> TextInputFormat` or custom format
> 4: string outputFormat, // SequenceFileOutputFormat (binary) or
> IgnoreKeyTextOutputFormat or custom format
> 5: bool compressed, // compressed or not
> 6: i32 numBuckets, // this must be specified if there are any
> dimension columns
> 7: SerDeInfo serdeInfo, // serialization and deserialization information
> 8: list<string> bucketCols, // reducer grouping columns and clustering
> columns and bucketing columns`
> 9: list<Order> sortCols, // sort order of the data in each bucket
> 10: map<string, string> parameters, // any user supplied key value hash
> 11: optional SkewedInfo skewedInfo, // skewed information
> 12: optional bool storedAsSubDirectories // stored as
> subdirectories or not
> } {code}
> The attached screenshot is an example comparing the before and after Table
> object of an ALTER_TABLE event that has trivial changes in StorageDescriptor.
> It just clears the field of 'storedAsSubDirectories:false', and that field
> defaults to be false. So actually makes no difference in the
> StorageDescriptor.
> I think we can compare changes in the StorageDescriptor and only reload file
> metadata if any of these changes:
> * 'location'
> * 'storedAsSubDirectories'
> Note that the default of 'storedAsSubDirectories' is false so removing
> 'storedAsSubDirectories:false' is considered as unchanged.
> CC [~hemanth619], [~csringhofer]
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