It seems that MockNodes created by the MockNetwork are able to persist data without H2 (or some other in-memory DB). Is this just an in-memory class? Or are mock nodes spinning up an H2 instance in the background somewhere?
Where is this defined in the Corda OS codebase? I've looked through MockNetwork, InternalMockNetwork, MockNode, TestStartedNode, MockNodeParameters.
Generally speaking each Corda class which stores data of any kind has a parallel implementation which uses mock storage. For example the MockTransactionStorage uses an in memory HashMap for storing transaction objects: https://github.com/corda/corda/blob/release/os/4.3/testing/node-driver/src/main/kotlin/net/corda/testing/node/internal/MockTransactionStorage.kt
A second example would be MockAttachmentStorage which uses a HashMap to store files: https://github.com/corda/corda/blob/release/os/4.3/testing/test-utils/src/main/kotlin/net/corda/testing/services/MockAttachmentStorage.kt
Related
We have a Azure data warehouse db2(Azure Synapse) that will need to be consumed by read only users around the world, and we would like to replicate the needed objects from the data warehouse potentially to a cosmos DB. Is this possible, and if so what are the available options? (transactional, merege, etc)
Synapse is mainly about getting your data to do analysis. I dont think it has a direct export option, the kind you have described above.
However, what you can do, is to use 'Azure Stream Analytics' and then you should be able to integrate/stream whatever you want to any destination you need, like an app or a database ands so on.
more details here - https://learn.microsoft.com/en-us/azure/sql-data-warehouse/sql-data-warehouse-integrate-azure-stream-analytics
I think you can also pull the data into BI, and perhaps setup some kind of a automatic export from there.
more details here - https://learn.microsoft.com/en-us/azure/sql-data-warehouse/sql-data-warehouse-get-started-visualize-with-power-bi
I'm quite new in c# and Xamarin android and I want to backup and restore my offline SQLite database created with sqliteOpenHelper Class, send and use that on another device. thanks in advance.
In Android API sets, the providers for SQLite library are available under, android.database.sqlite package. The most prominent types in the package are:
1. SQLiteOpenHelper: This is the main class that you need to inherit your classes from, in order to handle the database creation, opening or closing events. Even the events such as create new tables, or deleting the old tables and upgrading your databases to a latest version (such as upgrading the schema), are all handled here in this class-derived classes of yours.
2. SQLiteDatabase: This is the object that you get and use to either push the data to the database, or to read the data from the database.
3. SQLiteCursor: This is the cursor implementation for working with the data records that are returned after Query commands.
The way they all communicate is that, the main class for the data manipulation first of all inherits from SQLiteOpenHelperto get the functions to handle, then later has a field of type SQLiteDatabasein it to execute the functions for writing or reading the data.
For more information, you can check:
https://basicsofwebdevelopment.wordpress.com/2017/02/19/learning-sqlite-databases-in-xamarin-for-android/
https://www.c-sharpcorner.com/article/xamarin-android-develop-sqlite-database-using-sqliteopenhelper/
Is corda support state deletion scenario when don't need to use some state (in both dev/prod)
Because I face exception when start node like "class not found exception", It's happen when I delete state class in project and use same old persistence file.
I think it because of state class already insert in VAULT_STATES and it can't find that class when start node.
I expect to have some method that provide state deletion.
More info
In Dev side I delete persistence file and of course it's work, but I just worry about Production side.
As of Corda 3, if a node has a state stored as part of a transaction in its transaction storage or in its vault, the node needs to keep the state's class definition on its classpath permanently.
You can delete old transactions and states directly via the node's database, but only if the transactions are not required for transaction resolution. You would do this by dropping rows from the NODE_TRANSACTIONS and VAULT_STATES tables in the node's database (as well as any custom tables defined by the state's schemas if it is a QueryableState). However, if the deleted transactions are later required as part of transaction resolution, your node will throw an error.
Future versions of Corda may provide a mechanism to delete old or "non-current" states and transactions. You can find a discussion of what this process may look like here: https://groups.io/g/corda-dev/topic/20405353.
For development purposes you can simply just delete the persistence.mv.db file which is the entire H2 database. This will reset your corda node.
Of course don't do that for any production use.
does anybody know where OpenStack Swift stores the "Rings"? Is there a distributed algorithm or is it just one table somewhere on some of the Storage Nodes with information about all (!) the physical object locations (I cannot believe that because from my understanding of Object Storage, it should scale to Exabytes, and this would need lots of entries in such a table...)?
This page could not help me: http://docs.openstack.org/developer/swift/overview_ring.html
Thanks in advance for your help!
Ring Builder
The rings are built and managed manually by a utility called the ring-builder. The ring-builder assigns partitions to devices and writes an optimized Python structure to a gzipped, serialized file on disk for shipping out to the servers. The server processes just check the modification time of the file occasionally and reload their in-memory copies of the ring structure as needed.
so, it's stored in all servers.
If you were asking the path of ring,gz files it is under /etc/swift by default
Also these ring files are can be updated using the .builder files when swift rebalance is run.
I am creating cloud formation script, which will have ELB. In Auto Scaling launch configuration, I want to add encrypted EBS volume. Couldn't find an encrypted property withing blockdevicemapping. I need to encrypt volume. How can I attach an encrypted EBS volume to an EC2 instance through auto scaling launch configuration?
There is no such property for some strange reason when using launch configurations, however it is there when using blockdevicemappings with simple EC2 instances. See
launchconfig-blockdev vs ec2-blockdev
So you'll either have to use simple instances instead of autoscaling groups, or you can try this workaround:
SnapshotIds are accepted for launchconf blockdev too, and as stated here "Snapshots that are taken from encrypted volumes are automatically encrypted. Volumes that are created from encrypted snapshots are also automatically encrypted."
Create a snapshot from an encrypted empty EBS volume and use it in the CloudFormation template. If your template should work in multiple regions then of course you'll have to create the snapshot in every region and use a Mapping in the template.
As Marton says, there is no such property (unfortunately it often takes a while for CloudFormation to catch up with the main APIs).
Normally each encrypted volume you create will have a different key. However, when using the workaround mentioned (of using an encrypted snapshot) the resulting encrypted volumes will inherit the encryption key from the snapshot and all be the same.
From a cryptography point of view this is a bad idea as you potentially have multiple, different volumes and snapshots with the same key. If an attacker has access to all of these then he can potentially use differences to infer information about the key more easily.
An alternative is to write a script that creates and attaches a new encrypted volume at the boot time of a instance. This is fairly easy to do. You'll need to give the instance permissions to create and attach volumes and either have installed the AWS CLI tool or a library for your preferred scripting language. One you have that you can, from the instance that is booting, create a volume and attach it.
You can find a starting point for such a script here: https://github.com/guardian/machine-images/blob/master/packer/resources/features/ebs/add-encrypted.sh
There is an AutoScaling EBS Block Device type which provides the "Encrypted" option:
http://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-properties-as-launchconfig-blockdev-template.html
Hope this helps!
AWS recently announced Default Encryption for New EBS Volumes. You can enable this per region via
EC2 Console > Settings > Always encrypt new EBS volumes
https://aws.amazon.com/blogs/aws/new-opt-in-to-default-encryption-for-new-ebs-volumes/