Recent posts

“ASH math” of time_waited explained with pictures and simulation

As explained by John Beresniewicz, Graham Wood and Uri Shaft in their excellent overview ASH architecture and advanced usage, avg( v$active_session_history.time_waited ) is not a correct estimate of the average latency (the “true average”) esperienced by a wait event, the reason being...
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Fast refresh of aggregate-only materialized views with MAX – algorithm

In this post I will illustrate the algorithm used by Oracle (in 11.2.0.3) to fast refresh a materialized view (MV) containing only the MAX aggregate function: create materialized view test_mv build immediate refresh fast on demand with rowid as select gby as mv_gby, count(*) as...
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Fast refresh of aggregate-only materialized views with SUM – algorithm

In this post I will illustrate the algorithm used by Oracle (in 11.2.0.3) to fast refresh a materialized view (MV) containing only the SUM aggregate function: create materialized view test_mv build immediate refresh fast on demand with rowid as select gby as mv_gby, count(*) as...
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Fast refresh of aggregate-only materialized views – introduction

This post introduces a series about the algorithm used by Oracle (in 11.2.0.3) to fast refresh a materialized view (MV) containing only an aggregate: create materialized view test_mv build immediate refresh fast on demand with rowid as select gby as mv_gby, count(*) as...
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“alter session force parallel query”, and indexes

This post is a brief discussion about the advantages of activating parallelism by altering the session environment instead of using the alternative ways (hints, DDL). The latter ways are the most popular in my experience, but I have noticed that their popularity is actually due, quite frequently,...
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