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【学习】 2025年阅读清单

Oracle 19c Poor Performance With DataPump Export

2020-03-24

Oracle

Oracle DataPump Tips
- Reference
Oracle 19c Poor Performance With DataPump Tips

Reference

Poor Performance With DataPump Export On Large Databases (Doc ID 473423.1)

Data Pump Export Hanging In RAC At ESTIMATE Phase And Slow Performance (Doc ID 1948926.1)
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Oracle Exadata Smart Flash Cache Tips

2020-03-24

Oracle

Oracle Exadata Flash Tips
- Flash cache mode WriteThrough and WriteBack
Oracle Exadata Smart Flash Cache Tips

Flash cache mode WriteThrough and WriteBack

The default flash cache mode is WriteThrough on X4 and earlier systems.

Since April 2017, Oracle Exadata Deployment Assistant (OEDA) enables Write-Back Flash Cache by default if the following conditions are met:
1. GI and DB home must be 11.2.0.4.1 or higher 12.1.0.2 or higher 12.2.0.2 or higher AND
2. DATA diskgroup has HIGH redundancy
From Exadata Storage Server release 11.2.3.2.0, Exadata Smart Flash Cache can operate either as a Write-through cache or a Write-back cache. Write-through mode is best suited for random repeated reads commonly found in OLTP applications. Write-back mode is best suited for write-intensive applications.

Write-Through -> first write to physical disks and then to flash cache for faster reads. Write-Back -> first write to flash cache and then to physical disk for both faster reads and writes.
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Oracle 19c Wait event 'enq: KO - fast object checkpoint'

2020-03-18

Oracle

Oracle Event Tips
- wait event: ‘enq: KO - fast object checkpoint’
Oracle 19c Wait event ‘enq: KO - fast object checkpoint’

There were top event - ‘enq: KO - fast object checkpoint’ while I was doing awr report analysis, and found some test with it and some mos.

wait event: ‘enq: KO - fast object checkpoint’

From mos: Enq: KO - Fast Object Checkpoint Wait Event (Doc ID 2547319.1)
```
On reporting queries, there are too many "enq: KO - fast object checkpoint" wait event.

All reporting queries are doing full table scans concurrently. Oracle uses direct path reads instead of db file scattered reads. And direct path reads require a checkpoint

"_serial_direct_read"=NEVER
```
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Oracle 19c load awr report

2020-03-17

Oracle

Oracle awr Tips

Oracle 19c load awr report

Tips:

Load data from datapump file created by awrload.sql.

Use awrextr.sql extract data from AWR into a datapump file.

Use same db version is good choise(the awr format are different from db versions.)

Need to check tablespace’s size while load awr data due to the limit of tablespace.

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Oracle Recover Tips

2020-03-17

Oracle

Oracle Recover Tips

1.Recover oracle password file

Oracle Recover Tips

Tips:

1.Recover oracle password file

Wrong msg:

ERROR:
ORA-01017: invalid username/password; logon denied

Solution:

Use orapwd command to recover the password file.

orapwd file=$ORACLE_HOME/dbs/orapwORCL password=Welcome1 force=y  // force=y (if the password file is existed, will replace the password file instead by force)

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Oracle 19c Analysis SQL in AWR report Tips

2020-02-12

Oracle

Oracle SQLloader Tips
Oracle 19c Analysis SQL in AWR report

There are some sql in SQL ordered by CPU Time AWR report.

These sql were using so many cpu time…
```
/* SQL Analyze(0) */ select /*+ full(t) parallel(t, 6) parallel_index(t, 6) dbms_stats cursor_sharing_exact use_weak_name_resl dynamic_sampling(0) no_monitoring xmlindex_sel_idx_tbl no_substrb_pad */to_char...
 
```
What are these sqls? what are they doing?
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Oracle 19c online statistics gathering Tips

2020-02-11

Oracle

Oracle SQLloader Tips

Oracle 19c Online statistics gathering between sqlloader and insert append Tips

This is test with sqlloader/insert append sql.

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Oracle SQL loader Tips

2020-02-10

Oracle

Oracle SQLloader Tips scripts

Oracle SQL loader Tips

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Unix SSH Timeout Tips

2020-02-09

Unix

Unix SSH Tips

Unix SSH Timeout Tips

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Centos 7.6 + Postgresql 10 Install Tips

2020-02-03

Postgresql

Centos Postgres Postgresql Tips

Centos 7.6 + Postgresql 10 Install Tips

实战介绍在 CentOS 7.6 环境下如何源码安装 Postgresql 10

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Ubuntu Change default editor Tips

2019-12-01

Unix

Unix Tips

1. Modify .bashrc
2. Modify OS config editor
3.remove other editors

Ubuntu Change default editor Tips

1. Modify .bashrc

$ echo export EDITOR=/usr/bin/vim >> ~/.bashrc 

2. Modify OS config editor

$ update-alternatives --config editor 
-> 3 (vim.basic)

root@inst-hk01:~# update-alternatives --config editor 
There are 4 choices for the alternative editor (providing /usr/bin/editor).

  Selection    Path                Priority   Status
------------------------------------------------------------
  0            /bin/nano            40        auto mode
  1            /bin/ed             -100       manual mode
  2            /bin/nano            40        manual mode
* 3            /usr/bin/vim.basic   30        manual mode
  4            /usr/bin/vim.tiny    10        manual mode

Press <enter> to keep the current choice[*], or type selection number: 3
root@inst-hk01:~# 

3.remove other editors

$ sudo apt-get remove nano

test

$crontab -e

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Oracle Linux pstack Tips

2019-10-16

Oracle

Oracle Tips 12c pstack trace
- Install pstack in Oracle Linux 7.
Oracle Linux pstack Tips

Install pstack in Oracle Linux 7.

Install gdb by yum and there are pstack and gstack in gdb.
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Reference

Flash cache mode WriteThrough and WriteBack

wait event: ‘enq: KO - fast object checkpoint’

1.Recover oracle password file

1. Modify .bashrc

2. Modify OS config editor

3.remove other editors

Install pstack in Oracle Linux 7.