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    Maxwell Miranda
    Oracle DBA Consultant.
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    November 2009
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    • Foreign Keys deferred vs disabled
      Here is my observation regarding deferred foreign keys which I am not able to understand: - We have 3 tables : TP1, TC1 & TC2. TC1 and TC2 have foreign keys pointing to TP1 and foreign keys are defined as DEFERRED. - We load huge amounts of data to these tables once a week and the insert takes unusually long time. This is how we insert: (Case 1) step 1: […]
      Hi Friends, While analysing the AWR report of Oracle 11g, In PGA TARGET Advisory i found low est_pga_cache_hit_percentage at size_factor =1. If I increase the PGA_AGGREGATE_TARGET size will it improve the performance of the queries that accessing SORT/MERGE/HASH paths. or Should i found the queries accessing SORT/MERGE/HASH paths and tune them? Which will be […]
    • Oracle Performance
      Hello Please I am actually using a new server on Linux Redhat with 32G (64 bits) . I need some advice to increase performance since my rman takes Now 2 hours instead of 1 hour before when I was on 16G See below pfile details Code: --------- rwddb.__db_cache_size=1577058304 rwddb.__java_pool_size=33554432 rwddb.__large_pool_size=16777216 rwddb.__shared_pool_s […]
    • New to DBA
      Hi all, Hope this is the right place to post this question. I recently joined a program that prepares students to become DBA's. Its a six month program, roughly. It's every weekend sat-sun, 4-7 P.M. I wanted to attach our course schedule and get some feedback from you guys to see if the topics covered in this course would prepare me for an actual j […]
    • Oracle Import / Export help
      Hi, I am learning Oracle export/import options and I wanted to find a way as stated I have a destination database that I want to import a dump file to but exclude some schemas. I exported schemas using expdp user1/pass full=Y dir=tmp dumpfile=node1.expdp.dmp on the target node, I want to import full db excluding sys,system,dbsnmp schemas. is there an option […]
    • Bit confused with Select Query
      I am bit confused regarding below query . select /*+ parallel_index(t,"IDX_CR_TRANSACTION_HIST_17",32) dbms_stats cursor_sharing_exact use_weak_name_resl dynamic_sampling(0) no_monitoring no_expand index_ffs(t,"IDX_CR_TRANSACTION_HIST_17") */ count(*) as nrw,count(distinct sys_op_lbid(52330892,'L',t.rowid)) as nlb,count(distinct […]
    • Email using cron job
      Hi, Because of the daily task to monitor session in oracle database, I would like to set this task in crontab to run everyday and automatical send the output of the query. Do you have sample script for this? Thanks
    • explain plan for partition table
      explain plan for partition table hello, i have a question about explain plan for partition table. i have created two tables, one of them is partitioned and the other one is not. when i execute a query for analyzing the two tables and ask for the explain plans i am not sure what does ROW and BYTE mean? below i wrote two examples from the same query where in t […]
    • How to manage CLOB tables
      Hi..We have a table. Which has 4 columns. 1.ID column,2.CLOB column(which contains file information),3.Create Date,4.Create BY. Inserting data in this row is increasing exponenetially. Currently the size of this table is 400GB. Now to manage this table we have decided to delete some data in every year. But as deleting doesn't free up the space for CLOB […]

A little additional info on hc_ files:

“Q1: What is the $ORACLE_HOME/dbs/hc_.dat file?
A1: The $ORACLE_HOME/dbs/hc_.dat is created for the instance health check monitoring. It contains information used to monitor the instance health and to determine why it went down if the instance isn’t up. The file will be recreated at every instance startup.

Q2: What happens if the $ORACLE_HOME/dbs/hc_.dat file is deleted?
A2: Per Bug 4645405 UNABLE TO START DB – ORA-7445 [KSIHSMRINI()+152] [SIGBUS],
if you replace the file with an empty “dummy” copy, you will get an ORA-7445 error. Therefore, if the file gets deleted on the fly while the database is up, or if the file is replaced with a 0 byte file, simply delete the file and restart the database. The file will be correctly recreated at the next database startup.”

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