Re: PG index architecture

On 7/15/2014 1:26 PM, Andy Colson wrote:
> As I understand indexes, they are a key value pair, that contain a
> value and a position.  You lookup the value then use the position to
> seek into the database to load the record.

indexes are stored as a B-tree.  each terminal node has a block number
for the target record.

>
> Do we, or could we, load all the the matching index records, then sort
> them by position?  (maybe not all, maybe large batches)
>

b-trees are inherently ordered.   data records, however are not.


> When loading from the database, if access was slightly more sequential
> (vs very random), would it increase performance?
>
> Said another way:
>
> I think of table scanning as sequential, and fast.  That would be
> loading db record 1,2,3, etc.

database tables are unordered sets, there is no record 1,2,3.

>
> Would it be faster to load db records "mostly sequential": 1,3,4,7,10
> compared to randomly: 7,3,10,1,4

its unclear to me what you mean here.


--
john r pierce                                      37N 122W
somewhere on the middle of the left coast