[SPARK-11243] [SQL] zero out padding bytes in UnsafeRow

[davies]

For nested StructType, the underline buffer could be used for others before, we should zero out the padding bytes for those primitive types that have less than 8 bytes.

cc @cloud-fan

[cloud-fan]

LGTM, pending test

[rxin]

Is this different from a single

Platform.putLong(holder.buffer, offset, value);

?

[rxin]

nvm.

Can we add some unit test to test this behavior?

[davies]

Will add one tmr.

[SparkQA]

Test build #44132 has finished for PR 9217 at commit 12613bd.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds the following public classes (experimental):\n * class MutableUnsafeRow(val writer: UnsafeRowWriter) extends GenericMutableRow(null)\n

[rxin]

@davies did you have a chance to add a test case yet?

[SparkQA]

Test build #44204 has finished for PR 9217 at commit cf01d6d.

• This patch fails Scala style tests.
• This patch merges cleanly.
• This patch adds the following public classes (experimental):\n * class MutableUnsafeRow(val writer: UnsafeRowWriter) extends GenericMutableRow(null)\n

[SparkQA]

Test build #44207 has finished for PR 9217 at commit 9ff3f66.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[rxin]

Thanks. I've merged this.