MySQL - DBA Toolkit - Table Size and Growth

Table Size: Know What Is Taking Up Your Disk

Disk does not fill up overnight. It fills up gradually, driven by a handful of tables that nobody is watching — logging tables, audit tables, event history tables that grow without bound until they become a problem.

Knowing the size of your tables by schema is basic DBA hygiene. The data-to-index ratio tells you whether your indexes have grown disproportionately. The reclaimable space tells you how much fragmentation has built up from deletes and updates — space InnoDB holds but the OS cannot see.

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Reading the Results

Per-Table View

Column	What to Check
`table_rows`	Estimated row count from `information_schema` — approximate, not exact
`data_mb`	Size of actual row data
`index_mb`	Space used by all indexes on this table
`total_mb`	Combined footprint — what the table is costing on disk
`reclaimable_mb`	Space held by InnoDB but not containing live data — freed by `OPTIMIZE TABLE`
`index_to_data_pct`	Index size as a percentage of data size — over 100% is worth investigating

Schema Rollup

Use the second query to quickly identify which schemas are growing fastest or consuming the most space. A schema with a small table count but large total_mb usually has a few problem tables worth drilling into.

What to Watch For

Signal	What It Means
`reclaimable_mb` >> `data_mb`	Heavy delete/update churn — `OPTIMIZE TABLE` will reclaim space
`index_to_data_pct` > 100%	Indexes are larger than the data they cover — possibly too many or too wide
Large `table_rows` with small `total_mb`	Very narrow rows — often fine, but watch for hidden large columns (TEXT/BLOB)
Unexpected large table in a schema	Logging or audit table growing without a retention policy
Schema with rapidly growing `total_mb`	May need archival strategy or partitioning before it becomes a disk incident

table_rows in information_schema is an estimate based on InnoDB statistics. For exact counts run SELECT COUNT(*) FROM table_name — but be careful on large tables.

Gareth Winterman