> It certainly works quickly for smaller tables, however the 21.7 million
> record table I ran this on takes a touch longer as shown here:
>
> database=# explain select count(*) from table;
> NOTICE: QUERY PLAN:
>
> Aggregate (cost=478056.20..478056.20 rows=1 width=0)
> -> Seq Scan on table (cost=0.00..423737.76 rows=21727376 width=0)
>
> EXPLAIN
>
> However I noted explain provides rows as part of it's data; from what
> I've seen this loses precision over time or with large data imports,
> though; at least until the table is vacuumed again.
I guess I was saying that an index scan could take longer because it has
to walk the btree. However it only has one column of the table, so it
may be faster. I never measured the two, but the heap access needed for
the index scan currently is a performance killer. Sequential is faster
than all those random heap lookups from the index.
-- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610)
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