Snapshots are a batch-based approach to change data capture. The dbt snapshot command must be run on a schedule to ensure that changes to tables are actually recorded! While individual use-cases may vary, snapshots are intended to be run between hourly and daily. If you find yourself snapshotting more frequently then that, consider if there isn't a more appropriate way to capture changes in your source data tables. When the schema of your source query changes, dbt will attempt to reconcile the schema change in the destination snapshot table.
It will also not change the type of a column beyond expanding the size of varchar columns. That is, if a string column is changed to a date column in the snapshot source query, dbt will not attempt to change the type of the column in the destination table. Snapshots break this paradigm due to the nature of the problem that they solve. Because snapshots capture changes in source tables, they need to be running constantly in order to record changes to mutable tables as they occur.
As such, it's typical to only have one snapshot table per data source for all dbt users, rather than one snapshot per user.
Working with snapshots in Parallels Desktop for Mac
In this way, snapshot tables are more similar to source tables than they are to proper dbt models. This column can be used to order the different "versions" of a record. A list of columns to check for changes, or all to check all columns. Configs dbt-wide configs like tags , or warehouse-specific configs are supported in Snapshot configuration. The snapshot strategy to use.
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One of timestamp or check. If using the timestamp strategy, the timestamp column to compare. If you want to delete a snapshot or if you want to restore the data from a snapshot to a persistent disk, see Restoring and deleting persistent disk snapshots. To perform this task, you must have the following permissions. You can create snapshots from disks even while they are attached to running instances. Snapshots are global resources , so any snapshot is accessible by any resource within the same project. You can also share snapshots across projects. Note that snapshots are different from public images and custom images , which are primarily used to create boot disks for instances or to configure the boot disks for instance templates.
Snapshots are incremental and automatically compressed, so you can create regular snapshots on a persistent disk faster and at a much lower cost than if you regularly created a full image of the disk. Incremental snapshots work in the following manner:. This repeats for all subsequent snapshots of the persistent disk. Snapshots are always created based on the last successful snapshot taken. Compute Engine stores multiple copies of each snapshot across multiple locations with automatic checksums to ensure the integrity of your data. Use IAM roles to share snapshots across projects.
To see a list of snapshots available to a project, use the gcloud compute snapshots list command:.
To list information about a particular snapshot, such as the creation time, size, and source disk, use the gcloud compute snapshots describe command:. When you create a snapshot , you can specify a storage location. The location of a snapshot affects its availability and can incur networking costs when creating the snapshot or restoring it to a new disk. Snapshots can be stored in either one Cloud Storage multi-regional location , such as asia , or one Cloud Storage regional location , such as asia-south1. A multi-regional storage location provides higher availability and might reduce network costs when creating or restoring a snapshot.
For example, creating a disk from a snapshot stored in a multi-regional location does not incur network costs as long as the new persistent disk is created in one of the regions of the multi-regional group. A regional storage location gives you more control over the physical location of your data because you specify a single region. If you do not specify a storage location for a snapshot, GCP uses the default location , which stores your snapshot in a Cloud Storage multi-regional location closest to the region of the source disk.
If you need to choose regional storage, or if you need to specify a different multi-regional location, store your snapshot in a custom location. If you do not specify a storage location, your snapshot is stored in the multi-region that is geographically closest to the location of your persistent disk. For example, if your persistent disk is stored in us-central1 your snapshot will be stored in the us multi-region by default.
However, a default location like australia-southeast1 is outside of a multi-region. The closest multi-region is asia. Creating or restoring a snapshot will generate network costs. Select a custom location to store your snapshot in a regional location, or if you need to specify a different multi-regional location. If you need to comply with corporate or government data-placement policies, store your snapshot in the nearest regional location that complies with these policies.
If your application is not deployed in part of a multi-region and you want to prioritize low networking costs over high snapshot availability, store your snapshot in the region where your source disk is located.
This will minimize networking costs for restoring and creating snapshots from that source disk. However, unlike a multi-regional storage location, a regional storage location will not store your data redundantly across multiple data centers, so your data might not be accessible if a large-scale disruption occurs. To ensure the availability of your data, you might also want to store a redundant snapshot in a second location. Selecting your snapshot storage location is vital to minimizing network costs.
If you store your snapshot in the same region as your source disk there is no network charge when you access that snapshot from the same region. If you access the snapshot from a different region, there is a network cost. Each cloned image child stores a reference to its parent image, which enables the cloned image to open the parent snapshot and read it.
A COW clone of a snapshot behaves exactly like any other Ceph block device image. You can read to, write from, clone, and resize cloned images. There are no special restrictions with cloned images.
Index of /snapshots
However, the copy-on-write clone of a snapshot refers to the snapshot, so you MUST protect the snapshot before you clone it. The following diagram depicts the process. Ceph only supports cloning for format 2 images i. The kernel client supports cloned images since kernel 3. Ceph block device layering is a simple process.
Creating and maintaining snapshots of file systems
You must have an image. You must create a snapshot of the image. You must protect the snapshot. Once you have performed these steps, you can begin cloning the snapshot. The inclusion of the pool ID means that you may clone snapshots from one pool to images in another pool.
Image Template: A common use case for block device layering is to create a master image and a snapshot that serves as a template for clones. For example, a user may create an image for a Linux distribution e. Periodically, the user may update the image and create a new snapshot e. As the image matures, the user can clone any one of the snapshots. Extended Template: A more advanced use case includes extending a template image that provides more information than a base image. For example, a user may clone an image e. Template Pool: One way to use block device layering is to create a pool that contains master images that act as templates, and snapshots of those templates.