Oracle has added JSON support from 12.1.0.2. At various locations, e.g. Oracle XML DB Developer's Guide, JSON Developer's Guide, Oracle recommends "whenever you store JSON data in a BLOB or CLOB column you turn on the LOB cache option for that column. This option is turned off by default." So if a column of a … Continue reading Buffer Cache Usage for a lob segment if cached
Month: February 2020
select sequence NEXTVAL slow?
By default, when a sequence is defined, if the options "cache" or "nocache" is specified, Oracle will cache 20 sequence numbers. Usually that will be fine for most of circumstances. However you may see sometimes the following query running slow when getting the next value: select sequence_test.nextval from dual; It could take dozens of seconds … Continue reading select sequence NEXTVAL slow?
Timing a command on Windows?
On *nix system, we can use the command "time" to measure a command execution time. How do I do this on Windows? Fortunately there is a Powershell command "Measure-Command" for this. PS C:> Measure-Command {certutil -hashfile .\tmuninst.ini | Out-Host}SHA1 hash of file .\tmuninst.ini:7c 85 c2 94 73 8d 25 3e 12 8b eb 7a 1d … Continue reading Timing a command on Windows?
Show difference of two files side by side?
I use the command "diff" almost every day to compare files and see difference. I've never thought about fancy features of "diff" until today. Here is the story. I've copied 203 huge files -- 12T in total over the network and would like to see if any files are corrupted. So I did a check … Continue reading Show difference of two files side by side?
SSH session disconectted with “Write Failed: broken pipe”
If you are like me working on *nix systems remotly on your daily life, you might have seen this error "Write Failed:broken pipe" before when you ssh hop to a different server from your current *nix terminal session. It's annoying when this happens -- you lose your connection to the remote system and you have … Continue reading SSH session disconectted with “Write Failed: broken pipe”
Oracle ADR partition full due to large trace files
If you have an Oracle database 12c (12.2.0.1+) system, you may notice the size of the partition where ADR resides increases rapidly. And when you dig into it, you will find most of space is likely used by trace files. Basically there are two issues since Oracle 12.2.0.1: Large size of trace files created during … Continue reading Oracle ADR partition full due to large trace files
Input/output error — Rebooting Linux remotely
A few days ago, while I was doing an Oracle RMAN duplicate operation to set up another database on a Oracle Linux 6.10 system running on VMWare, the sytem went into a kernel panic state with the following messages: kernel:[217869.366586] NMI watchdog: BUG: soft lockup - CPU#8 stuck for 223s! [sadc:32354] kernel:[217869.366598] NMI watchdog: BUG: … Continue reading Input/output error — Rebooting Linux remotely
Linux cannot start due to a mistake in fstab?
You have a new disk and you create partitions on it and modify the fstab. Reboot the OS and it won't boot due to an wrong entry in fstab. Usually on the console screen, you will be prompt to enter single user mode as the root user. What you need to do is correct the … Continue reading Linux cannot start due to a mistake in fstab?
CIFS mount : special device does not exist
Recently we had an VM Oracle Linux server 6.9 crashed and we have had to rebuild the server from the scratch. This server has a CIFS mount for Oracle database backup. After we re-created the sever with a newer OVA which is on Oracle Linux server 6.10, we could not mount the CIFS share anymore. … Continue reading CIFS mount : special device does not exist
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