Take MySQL Column Type Into Account in VStreamer

[mattlord]

Description

In #7969 we added right side null-byte padding to BINARY columns after processing the binlog event in order to match the MySQL behavior and value so that we correctly calculate the keyspace IDs for BINARY columns in vindex functions like binary_md5 and correctly apply vreplication filters using those columns.

It turns out, however, that row based binlog events make no distinction between a BINARY(4) column and a CHAR(4) column with a binary collation like utf8mb4_bin (you can see a detailed discussion here). So after #7969 we were also, incorrectly, adding right side null-byte padding to CHAR columns with binary collations.

Although we ensured we did not add more padding than the actual column would hold in #8730, we really shouldn't be adding any padding at all to CHAR columns in order to match the MySQL behavior (otherwise we have discrepancies as described here). But in order to do this we needed to thread the target MySQL column type info through the vstreamer and RBR binlog event processing components so that we ONLY add the padding to values for actual BINARY columns and nothing else (CHAR columns being the known problematic case today).

Now we only add the padding if the underlying MySQL column on the target is BINARY and then it’s just bytes, not chars made of up N bytes, so the subsequent pad trimming based on the charset was removed.

The manual test case here also now passes in this branch:

vitess@163dba62a8fb:/vt/local$ mysql -h 127.0.0.1 -P 15306 customer -e "select customer_id, hex(md5) from customer;"
+-------------+------------------------------------------------------------------+
| customer_id | hex(md5)                                                         |
+-------------+------------------------------------------------------------------+
|           1 |                                                                  |
|           2 | 6132613733393661326666396365333930373461613932643233663339633362 |
|           3 |                                                                  |
|           4 | 6132613733393661326666396365333930373461613932643233663339633362 |
+-------------+------------------------------------------------------------------+

vitess@163dba62a8fb:/vt/local$ vtctlclient -server localhost:15999 VDiff customer.commerce2customer
Summary for table customer:
	ProcessedRows: 4
	MatchingRows: 4
	MismatchedRows: 0
	ExtraRowsSource: 0
	ExtraRowsTarget: 0
Summary for table corder:
	ProcessedRows: 0
	MatchingRows: 0
	MismatchedRows: 0
	ExtraRowsSource: 0
	ExtraRowsTarget: 0

vitess@163dba62a8fb:/vt/local$ vtgate --version
Version: 13.0.0-SNAPSHOT (Git revision 3ff9fbdad7 branch 'NullBytePaddingFinalFinal') built on Thu Dec  9 04:04:01 UTC 2021 by vitess@09daf1423251 using go1.17 linux/amd6

Related Issue(s)

Fixes: #9207

Checklist

• Should this PR be backported? Yes, to 12.0
• Tests were added
• Documentation is not required

[rohit-nayak-ps]

lgtm.
Very nice! An elegant solution to another binlog parser edge case.

[deepthi]

Very thorough code comments and nice test case. 💯