Known limitations about gh-ost

[shlomi-noach]

• Does not support FOREIGN KEYS of any kind (table must be neither "parent" nor "child")

  may support in the future

• Active-active writable-writable master-master should not be supported (or provide a flag --allow-master-master?) Need to further think over this one

  master-master is supported, but requires the user to add --allow-master-master. gh-ost will not verify whether this is an active-active or an active-passive setup. An active-active setup may present some problems, that we haven't fully figured out yet. active-passive is good to go.

[shlomi-noach]

• with go-mysql client, table names turn to lower case on reading RBR. This means potentially no support for tables with identical names but differing case. To clarify, you may not be able to alter MyTable if you also have MYtable table.

[shlomi-noach]

• When altering a table, some sort of UNIQUE KEY must be shared between the two tables.

  in the case where you have a table with a unique key but no primary key, and you wish to convert the uk to pk, two migrations are required: one to add pk, utilizing the existing uk, another to drop the uk. Maybe in the future gh-ost will support this as a single operation.

• Shared UNIQUE KEY must not include columns with NULL values. That is: it is OK for columns to be NULLABLE, but not OK if they actually contain NULL values.

  • For PRIMARY KEYs this is a non issue since by definition they may only include non-nullable columns

[shlomi-noach]

• Currently no support for renaming a column

  There is now.

[shlomi-noach]

This issue turns into a documentation page: requirements and limitations. Closing