Hey folks, I've started working on a few patches to add "guard rails" to various user-specified dimensions in Kudu. In particular, I'm planning to add limits to the following:
- max number of columns in a table (proposal: 300) - max replication factor (proposal: 7) - max table name or column name length (proposal: 256) - max size of a binary/string column cell value (proposal: 64kb) The reasoning is that, even though in some cases we don't know a specific issue that will happen outside these limits, we've done very little testing (and have no automated testing) outside of these ranges. In some cases, we do know that there is a certain threshold that will cause a big problem (eg large cell sizes can cause tablet servers to crash). In other cases, it's just "unknown territory". In all cases, I'm planning on making the limits overridable via an "unsafe" configuration flag. That means that a user can run with "--unlock_unsafe_flags --max_identifier_length=1000" if they want to, but they're explicitly accepting some risk that they're entering untested territory. Of course, in all cases, if we hear that there are people who are bumping the maxes higher than the defaults and having good results, we can consider raising the maximum, but I think it's smarter to start conservatively low and raise later as we increase test coverage. Also, I'm sure down the road we'll add features such as BLOB support or sparse column support, and at that time we can remove the corresponding guard rails. I'm sending this note to both user@ and dev@ to solicit feedback. Are there any other dimensions people can think of where we should probably add guard-rails? Is anyone out there already outside of the above ranges and can make a case that we're being too conservative? Thanks -Todd -- Todd Lipcon Software Engineer, Cloudera
