Re: Why need a lock?

[Tom Lane]

jacktby jacktby <jack...@gmail.com> writes:
> I find this in source code
> #define ShareLock                             5       /* CREATE INDEX 
> (WITHOUT CONCURRENTLY) */
> I think if there is no CONCURRENTLY, so why we need a lock, I think that’s 
> unnecessary. What’s the point?

We need a lock precisely to prevent concurrent execution
(of table modifications that would confuse the index build).

                        regards, tom lane