Question for WOS and ROS

Qi_Zhou

HI,  from the Vertica documentation I got to know that insert statement(without direct distinct) will load data to WOS first, then the tuple move will merge the WOS data to ROS files,  when we read data by exeucting select,  it will always read data from ROS since the data in ROS is sorted.   But Tuple move will merge data every 10 minutes by default,  that means if I insert a record in to WOS, I might have to wait 10 minutes so that i could get it from select statement only after 10 minutes,  actually, this is not the case,  so I'm wondering maybe some of my understanding from the documentation is wrong?  Thanks.

Qi_Zhou

one more question,  since tuple move will move data from WOS to ROS every 10 minutes, what if the WOS crashed before it get chance to save its data to ROS and those data were already committed in client side?  

[Deleted User]

Hi, 

Your first question, when you do select Vertica reads from ROS and WOS. 
Second, if your node crashes before the data got committed to disk, if you have a 3 nodes cluster this node will recover he information from their "buddies" nodes. Other wise you will lose that data until the last good epoch that was committed to disk. 

Hope this answer your questions, 

Regards, 
Eugenia

wwong2

HI, in regards to timing, take a look at the tuple mover configuration parameters
MergeOutInterval - The number of seconds the Tuple Mover waits between checks for new ROS files to merge out. If ROS containers are added frequently, you may need to decrease this value.
Default Value: 600

MoveOutInterval - The number of seconds the Tuple Mover waits between checks for new data in the WOS to move to ROS.
Default Value: 300

Also, depending on the size of your load, if it is large load, would recommend loading them directly into ROS containers using the direct keyword.

Regards


 

[Deleted User]

Hi Qi,
Can you point me to the portion of the documentation you are referencing? Specifically about the select statement?

[Deleted User]

Hi Qi,
I found a similar question with a detailed response: https://community.vertica.com/vertica/topics/db_crash_suddenly_if_the_records_which_locate_in_wos_bu... hope this helps.

Qi_Zhou

Hi Eugenia Moreno Wayne Wong and Vicki,  thank you so much for your response, it's very helpful,  especially for the last link post, fully answer my question, thanks