Why Does phpMyAdmin Show Inconsistent Row Counts for InnoDB Tables?

Can't Trust the Row Count in phpMyAdmin?

In phpMyAdmin, you may encounter significant discrepancies in estimated row counts for tables that have remained unchanged. This puzzling inconsistency can be attributed to the underlying database engine's handling of row counting.

Unlike MyISAM tables, which maintain an accurate row count, InnoDB tables like the one in your example lack this feature. To determine the exact row count, InnoDB must painstakingly scan every single row in the table, making the SELECT COUNT(*) query computationally expensive for large tables.

phpMyAdmin utilizes a SHOW TABLE STATUS query to retrieve an estimated row count from InnoDB. This approximation, however, varies each time you execute it, potentially resulting in substantial deviations from the actual count.

The MySQL manual acknowledges this limitation: "For storage engines such as InnoDB, this value [from SHOW TABLE STATUS] is an approximation, and may vary from the actual value by as much as 40 to 50%."

For precise row counts, the manual recommends using SELECT COUNT(*). Additionally, the InnoDB documentation explains that concurrent transactions can result in different row counts being "seen" simultaneously, making internal row counting impractical.

Therefore, while SHOW TABLE STATUS may provide an estimate, it falls short of delivering absolute precision. For accurate and consistent row counting, consider implementing a counter table maintained by your application or utilizing the MySQL query cache to optimize performance.

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