Bug #116753 COMPRESSION_PERCENTAGE in binary_log_transaction_compression_stats is incorrect

• Submitted: 22 Nov 5:03
• Modified: 22 Nov 5:37
• Reporter: Ke Yu (OCA)
• Status: Analyzing
• Category: MySQL Server: Replication
• Severity: S3 (Non-critical)
• Version: 8.0.40
• OS: Any
• Assigned to: MySQL Verification Team
• CPU Architecture: Any

[22 Nov 5:03] Ke Yu

Description:
COMPRESSION_PERCENTAGE in binary_log_transaction_compression_stats is incorrect when the compression rate is very high.

How to repeat:
1. execute the following sql: 
mysql> select COMPRESSION_TYPE,TRANSACTION_COUNTER,COMPRESSED_BYTES_COUNTER,UNCOMPRESSED_BYTES_COUNTER,COMPRESSION_PERCENTAGE from performance_schema.binary_log_transaction_compression_stats;
+------------------+---------------------+--------------------------+----------------------------+------------------------+
| COMPRESSION_TYPE | TRANSACTION_COUNTER | COMPRESSED_BYTES_COUNTER | UNCOMPRESSED_BYTES_COUNTER | COMPRESSION_PERCENTAGE |
+------------------+---------------------+--------------------------+----------------------------+------------------------+
| ZSTD             |             6032130 |               1494533417 |              1165338872550 |                    100 |
| NONE             |               90144 |              28623075567 |                28623075567 |                      0 |
+------------------+---------------------+--------------------------+----------------------------+------------------------+
2 rows in set (0.00 sec)

2. The COMPRESSION_PERCENTAGE is 100, but UNCOMPRESSED_BYTES_COUNTER/COMPRESSED_BYTES_COUNTER = 779.
COMPRESSION_PERCENTAGE does not reflect the true compression rate.

Suggested fix:
I expect to change COMPRESSION_PERCENTAGE to UNCOMPRESSED_BYTES_COUNTER/COMPRESSED_BYTES_COUNTER not (1 - COMPRESSED_BYTES_COUNTER/UNCOMPRESSED_BYTES_COUNTER) * 100 .