The vacuum_freeze_min_age setting determines the youngest XID which will be changed to FrozenXID on data pages which are being vacuumed anyway. The advantage of setting it low is that far more XIDs will already be frozen when the data page is finall…
Introduction ------------ The Heap Only Tuple (HOT) feature eliminates redundant index entries and allows the re-use of space taken by DELETEd or obsoleted UPDATEd tuples without performing a table-wide vacuum. It does this by allowing single-page va…
5.3 Tuples and Sequences We saw that lists and strings have many common properties, e.g., indexing and slicing operations. They are two examples of sequence data types. Since Python is an evolving language, other sequence data types may be added. The…
[construction of tuples containing 0 or 1 items] the syntax has some extra quirks to accommodate these. Empty tuples are constructed by an empty pair of parentheses; a tuple with one item is constructed by following a value with a comma (it is not su…
below is a good answer for this question , so I copy on here for some people need it By the way, the three forms can be combined as follows: def f(a,*b,**c): All single arguments beyond the first will end up with the tuple b, and all key/value argume…
12.1 Tuples are immutable(元组是不可变的)A tuple is a sequence of values. The values can be any type, and they are indexed by integers, so in that respect tuples are a lot like lists. The important difference is that tuples are immutable.Syntactically, a tu…
