When we restart an Oracle database instance, does it delete all the data in the memory and kick a fresh start, or keep some information in the memory?
All memory that the instance had is cleared. In a RAC database that has multiple instances running, restarting one instance does not clear the memory from other instances.
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I want to clarify what I need install for standby, I am confusing with this, in primary all fine, but for standby I dont know what I need install first? please explain simple, for primary I installed database without dbca, but for standby I dont know.
Assuming you have a database (primary) already configured, running, etc, the steps are
On the primary
Create a Backup Copy of the Primary Database Data Files Create a
Control File for the Standby Database Create a Parameter File for the
Standby Database Copy Files from the Primary System to the Standby
System Set Up the Environment to Support the Standby Database
On the Standby
Start the Physical Standby Database
Verify the Physical Standby Database Is Performing Properly
In effect, the software plus the instance (ie, the parameters etc needed to start an instance in nomount mode) are what is required on the standby node. Then you will copy the datafiles from the primary to "flesh out" the database.
But all of this is documented really well in a step-by-step guide
https://docs.oracle.com/en/database/oracle/oracle-database/19/sbydb/creating-oracle-data-guard-physical-standby.html
I am planning to setup a small mongodb testing environment which consists of 6 physical servers and each server has 4 SSDs. My expectation is to maximize both I/O throughput and disk space utilization. After some reading and searching, it seems that MongoDB is only able to configure a single data folder for each instance. There are 3 possible solutions in my mind:
create a big volume on each server with RAID (e.g., RAID5 or RAID10).
for each disk on each server, create a mongo shard instance (or shard's replica).
start mongo instance with "--directoryperdb" parameter to store databases in seperate folders, and then use Linux symbol link to point the database folders to other disks.
Which deployment strategy is the most recommended way in a heavy loaded mongo production environment? Thanks.
for each disk on each server, create a mongo shard instance (or shard's replica).
You make no mention of RAM in your post, but running multiple Mongo instances on the same server will result in them competing for RAM.
start mongo instance with "--directoryperdb" parameter to store databases in seperate folders, and then use Linux symbol link to point the database folders to other disks.
No need to mess around with symbolic links, just mount the disks to the directory where Mongo puts each database.
I would either go for option 1 (RAID) or option 3 (databases on separate disks), but in either case some benckmarks would be a good idea before going into production.
I am using agentx++ to create shared tables.
After a snmpd restart, the subagent reconnects to the master agent but all rows in the shared tables are deleted.
Any Idea why the rows are deleted upon snmpd restart?
What kind of mechanism do you have for saving the data to DB? All row data may be kept in RAM during agent lifetime...
I recently signed up for Heroku's Redis To Go https://addons.heroku.com/redistogo. For now, I'm using the free Nano plan, which says:
5 MB Redis Instance
1 Database
Non-persistent
No Backups
10 Connections
I get what 'No Backups' etc. mean, but can't find any info on what is 'Non-persistent'? Does it mean the data is wiped out every time I deploy? Daily? Every now and then? When Heroku crashes?
Non-persistent means that your data will disappear if a restart of your instance is needed
e.g. Server issues caused by AWS usually involve instance restarts.
The other plans all provide AOF persistance and daily snapshot RDB backups of your data.
The Direct plans are 30% cheaper and you get more features.
More info on persistence and backups
If I stop an EC2 instance, rather than terminate, will this image be saved in my account and be available to be used at a later stage? ..as I noticed terminated instances eventually dissappear, would a stopped instance be available to boot up and start when ever?
Also regarding charging, I assume the cost for having a stopped instance would be charged per GB similar to a custom AMI?
Also another possibly simple question, if I shutdown a machine over SSH or via a script, does this initiate a termination or just a stop an instance (I assume it terminates the instance).
Thanks
If you terminate the EBS backed instance, it will remove it from the list of running instance, including it's allocated EBS volume. Unless you set the instance attribute not to delete the volume.
If you only stop, it will changed to stopped status and you can start it again later.
If you shutdown a machine, it default's to stop.
A good read to protect your instance see: http://alestic.com/2010/01/ec2-instance-locking
If you stop an instance based on EBS, then the instance will terminate automatically but you'll be charged for EBS storage until you delete the EBS.