[ewjordan]

Significantly altering an active table without downtime is a problem that will not, and should not, ever be solved by a library. It's too fraught with peril and special case fun for any competent devops person to leave it up to external code.

[nahname]

The work that goes into "external code" is higher quality than most companies can achieve. The cost of developing a similar tool may also be outside what the company can afford to invest.

If your business is online schema changes, then inventing it yourself makes sense. Otherwise you are likely throwing money away to create an inferior product.

[michaeldejong]

Agreed. But to be fair I've not yet encountered such a library/tool yet. All tools I've seen leave the active table alone, and simply create a new table, do all their work there, and finally somehow switch the two tables (either in naming or routing queries). Some even perform the work on a different database server.