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https://issues.apache.org/jira/browse/SPARK-55131?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Jungtaek Lim reassigned SPARK-55131:
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Assignee: Jungtaek Lim
> The default delimiter of StringAppendOperator (merge operator for RocksDB)
> conflicts when merge is used with non-existence value
> --------------------------------------------------------------------------------------------------------------------------------
>
> Key: SPARK-55131
> URL: https://issues.apache.org/jira/browse/SPARK-55131
> Project: Spark
> Issue Type: Bug
> Components: Structured Streaming
> Affects Versions: 4.2.0
> Reporter: Jungtaek Lim
> Assignee: Jungtaek Lim
> Priority: Major
> Labels: pull-request-available
>
> The default delimit of StringAppendOperator (merge operator for RocksDB)
> conflicts when merge is used with non-existence value.
> When there is an existing value, applying merge would be following:
> <size of the encoded value (4 bytes, big endian)><encoded
> value><delimiter><...>{color:#ff0000}<delimiter><size of the encoded
> value><encoded value>{color}
> *red color refers to the newly added content
> Reading the value would be straightforward, read the size, read the encoded
> value based on the size, skip one byte (for delimiter), loop.
> When there is no existing value, applying merge would be following:
> {color:#ff0000}<delimiter><size of the encoded value><encoded value>{color}
> Reading the value would not be the same with the case in above - we need to
> skip reading delimiter at the start to apply the same read logic.
> -That said, we need to ensure delimiter to be an "invalid value" of the first
> byte of the size.-
> -The value of default delimit is "," (44, 0x2C) which does not satisfy it.
> Since we do not allow negative value for the size, any value making the size
> (4 bytes) to be negative can be used as a delimiter.-
> ^ The above is dependent on the endianness and we tend to use sun's Unsafe
> module for putting some value into byte array & UnsafeRow which follows
> system's default endianness. The above is only safe when the system uses big
> endian, which is guaranteed by JVM but that's abstracted within JVM and
> Unsafe module breaks the abstraction. Making it worse, most common systems
> use little endian.
> Alternative is to ensure the delimiter to be available in the first byte of
> the value, regardless of whether the value is written from put vs merge.
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