cacheutil: caching size estimate is not valid

[ajwerner]

Describe the problem

cockroach/pkg/sql/cacheutil/cache.go

Lines 106 to 108 in 59701cf

	// Table version remains the same: update map, unlock, return.
	const sizeOfEntry = int(unsafe.Sizeof(entry))
	if err := c.boundAccount.Grow(ctx, int64(sizeOfEntry)); err != nil {

The const size there is always going to be 2 words. The value it points to may be much larger. In general, this whole scheme doesn't seem all that sound.

Jira issue: CRDB-20255

[ajwerner]

While we're here, the warning is going to get very noisy. Instead this thing should use LRU or something and evict. If it's going to log, it should rate limit that logging.