Dynamic sampling summary

In this post I'm going to summarize issues and strange behavior I've mentioned in my previous 2 posts: Oracle 11.2 Oracle 12.2 Empty stats Wrong stats Empty stats Wrong stats A single DYNAMIC_SAMPLING(10) hint Correct Wrong result Correct Wrong result A single DYNAMIC_SAMPLING_EST_CDN hint Almost correct Wrong result Almost correct Wrong result DYNAMIC_SAMPLING(10) and DYNAMIC_SAMPLING_EST_CDN … Continue reading Dynamic sampling summary

PDB Clone database serialization (12c case)

Here I am going to consider the mechnics for PDB Snapshot "clone database" process serialization, which prevents us from creating many PDBs simulteneously. (In ideal world you would like to create as much as you need PDBs for your unit tests on demand by several/many user sessions simulteneously but there are some limitations of this … Continue reading PDB Clone database serialization (12c case)

Dynamic sampling- wrong stats case

My usecase: Create 2 tables: T_BIG will be untouched T_SMALL - "global temporary table" will contain much more records than stats claims. spool 10 set lines 200 set pages 1000 DROP TABLE T_SMALL; DROP TABLE T_BIG; CREATE GLOBAL TEMPORARY TABLE T_SMALL ON COMMIT PRESERVE ROWS AS SELECT rownum id, rpad('a',1000,'b') pad FROM dual connect by … Continue reading Dynamic sampling- wrong stats case