https://bugzilla.wikimedia.org/show_bug.cgi?id=4715

--- Comment #64 from Sean Pringle <[email protected]> ---
The rev_comment field could be increased to 767 bytes without requiring changes
to the indexing for either stock Mediawiki or WMF databases. The same width
limit would apply to all of the varbinary comment fields. That would allow 191
characters minimum for a 4 byte charset.

`rev_comment` varbinary(767) DEFAULT NULL

767 is a internal key-width limit per column in InnoDB. Exceeding it would
block the use of covering indexes used on WMF databases for performance. 

Sounds like we could:

a) Choose to expand to a minimum of 191 characters
b) Decide whether comments should be entirely redesigned to be more flexible

My expectation is that (a) would not harm performance much, if at all, for
enwiki; currently there are various factors boosting performance besides the
original custom covering indexes. Eg, table partitioning on slaves handling
specific query groups, and quite simply a bunch more hardware :)

Such schema changes would take some weeks to roll out, but otherwise aren't
terribly painful. Certainly not a reason to avoid the issue.

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