<!here> Does Growthbook store data in DB related to assigned variation flag value to given user? like userId=123

inExperiment: true,
  variationId: 1,
  value: 'TEST_VAL_2',
  hashAttribute: 'id',
  hashValue: '333'

Does these information store in DB?

GrowthBook does not store that information. The SDKs have a trackingCallback you can define that lets you store that information yourself in your own database. Then, GrowthBook can query your database to analyze results

I actually want to search user and then override the flag value for specific user. is there any solution for this issue?

You can add a rule to a feature that forces a value to a specific user

Yes that is what I did now, but thinking about user list feature. BTW Where SDK store flag value for specific user? is it cache somewhere? if yes for how much time?

Instead of "is equal to" you can do "is in the list" and put a comma separated list of user ids. The SDKs just store the user attributes in memory. It's not persisted anywhere. So everytime you instantiate a new GrowthBook instance you need to pass the attributes in again.