skeema / skeema / 15478269041

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table size calculations: don't include DATA_FREE

A few Skeema options/features involve calculating the physical size of a
table:

* safe-below-size option (permit unsafe changes on tables below size)
* alter-wrapper-min-size option (bypass alter-wrapper on tables below size)
* alter-wrapper / ddl-wrapper command-lines using {SIZE} variable (generic way
  to pass the table size to any arbitrary wrapper script)

Skeema obtains table sizes from information_schema.tables metadata.
Previously, when calculating the size of a table, the math included DATA_FREE
in order to more closely align with physical ibd file sizes on disk.

However, upon further reflection, excluding DATA_FREE makes more sense for all
the use-cases above: the actual size of the data and indexes is what matters
for things like OSC tool execution duration, restoring an improperly-dropped
table from a logical backup, etc.

Furthermore, data_free is extremely inaccurate for partitioned tables. (The
MySQL manual suggests use of the I_S partitions table instead for calculating
data_free for partitioned tables, but those values are uselessly always zero,
see https://bugs.mysql.com/bug.php?id=113256)

For these reasons, this commit adjusts table size calculations to now
exclude DATA_FREE. This may affect size-related behaviors when operating on
tables with heavy DELETE workloads, but the change should generally be either
neutral or beneficial with regard to matching the intended behavior of the
size-related options.

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