Re: online index rebuilds - FFS or FTS
- From: Tanel Põder <tanel.poder.003@xxxxxxx>
- To: "Roger Xu" <roger_xu@xxxxxxxxxxx>, "ORACLE-L" <oracle-l@xxxxxxxxxxxxx>
- Date: Mon, 30 Jan 2006 15:43:40 -0600
Nope,
Index full scan traverses the index tree structure, from root to branch to
first (or last) leaf and follows pointers to next leaves block by block. A
serial index full scan will guarantee that the rows are returned in key
order from it, thus avoiding a later sorting step when using order by for
example.
Fast full index scan reads the whole index segment with multiblock reads
just as with full table scan, ignores branch blocks and returns whatever
keys it finds from there, no ordering is guaranteed. Index FFS can be
helpful when doing aggregate functions (sum, count, avg, etc) on indexed
column, because index segment is generally smaller than table, thus can be
scanned using fewer block gets/multiblock reads. However, when the indexed
colum is not marked as "NOT NULL" some aggregate functions such unrestricted
count(*) from table can't use it (as rows which have all indexed columns
NULLs, aren't stored in the index).
Tanel.
----- Original Message -----
From: "Roger Xu" <roger_xu@xxxxxxxxxxx>
To: "Jonathan Lewis" <jonathan@xxxxxxxxxxxxxxxxxx>;
<tanel.poder.003@xxxxxxx>; <joseph@xxxxxxxxxxxxxx>; "Bobak, Mark"
<Mark.Bobak@xxxxxxxxxxxxxxx>; "ORACLE-L" <oracle-l@xxxxxxxxxxxxx>
Sent: Monday, January 30, 2006 3:20 PM
Subject: RE: online index rebuilds - FFS or FTS
I thought "fast full index scan" was just another name for "index full
scan"?
-----Original Message-----
From: Jonathan Lewis [mailto:jonathan@xxxxxxxxxxxxxxxxxx]
Sent: Monday, January 30, 2006 2:06 PM
To: tanel.poder.003@xxxxxxx; Roger Xu; joseph@xxxxxxxxxxxxxx; Bobak,
Mark; ORACLE-L
Subject: Re: online index rebuilds
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