On Thu, Jan 27, 2011 at 2:12 PM, Igor Neyman <ineyman@xxxxxxxxxxxxxx> wrote: > > >> -----Original Message----- >> From: Scott Marlowe [mailto:scott.marlowe@xxxxxxxxx] >> Sent: Thursday, January 27, 2011 3:59 PM >> To: Mladen Gogala >> Cc: Igor Neyman; Tom Lane; David Wilson; Kenneth Marshall; >> pgsql-performance@xxxxxxxxxxxxxx >> Subject: Re: Postgres 9.0 has a bias against indexes >> >> On Thu, Jan 27, 2011 at 1:44 PM, Mladen Gogala >> <mladen.gogala@xxxxxxxxxxx> wrote: >> > On 1/27/2011 3:37 PM, Scott Marlowe wrote: >> >> >> >> On Thu, Jan 27, 2011 at 1:31 PM, Mladen Gogala >> >> <mladen.gogala@xxxxxxxxxxx> wrote: >> >>> >> >>> There is INDEX UNIQUE SCAN PK_EMP. Oracle will use an index. >> >> >> >> That's because Oracle has covering indexes. >> >> >> > I am not sure what you mean by "covering indexes" but I >> hope that for >> > the larger table I have in mind, indexes will be used. >> For a small >> > table like >> >> In Oracle you can hit JUST the index to get the data you need >> (and maybe rollback logs, which are generally pretty small) >> >> In Pgsql, once you hit the index you must then hit the actual >> data store to get the right version of your tuple. So, index >> access in pg is more expensive than in Oracle. However, >> updates are cheaper. >> Always a trade off >> >> > > Scott, > What you describe here isn't about "covering indexes" - it's about different ways implementing MVCC in Oracle and PG. It is about covering indexes AND it's about the difference in how MVCC is implemented in both databases. -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
