By using a timestamp range filter in the query, you can ensure that the analysts only see the customer data that is within the desired time range, regardless of the garbage collection policy1. This option is the most cost-effective and simple way to avoid fetching data that is marked for deletion by garbage collection, as it does not require changing the existing policy or creating additional jobs. You can use the Bigtable client libraries or the cbt CLI to apply a timestamp range filter to your read requests2.
Option A is not effective, as it increases the number of versions to 2, which may cause more data to be retained and increase the storage costs. Option C is not reliable, as it reduces the expiring values to 29 days, which may not match the actual data arrival and usage patterns. Option D is not efficient, as it requires scheduling a job daily to scan and delete the data, which may incur additional overhead and complexity. Moreover, none of these options guarantee that the data older than 30 days will be immediately deleted, as garbage collection is an asynchronous process that can take up to a week to remove the data3. References:
* 1: Filters | Cloud Bigtable Documentation | Google Cloud
* 2: Read data | Cloud Bigtable Documentation | Google Cloud
* 3: Garbage collection overview | Cloud Bigtable Documentation | Google Cloud

If you're running a performance test that depends upon Cloud Bigtable, be sure to follow these steps as you plan and execute your test:
Use a production instance. A development instance will not give you an accurate sense of how a production instance performs under load.
Use at least 300 GB of data. Cloud Bigtable performs best with 1 TB or more of data. However, 300 GB of data is enough to provide reasonable results in a performance test on a 3-node cluster. On larger clusters, use
100 GB of data per node.
Before you test, run a heavy pre-test for several minutes. This step gives Cloud Bigtable a chance to balance data across your nodes based on the access patterns it observes.
Run your test for at least 10 minutes. This step lets Cloud Bigtable further optimize your data, and it helps ensure that you will test reads from disk as well as cached reads from memory.
Reference: https://cloud.google.com/bigtable/docs/performance

To update a streaming pipeline with improved business logic and reprocess the previous two days of delivered Pub/Sub messages, you should use Pub/Sub Seek with a timestamp and Pub/Sub Snapshot capture two days before the deployment. Pub/Sub Seek allows you to replay or purge messages in a subscription based on a time or a snapshot. Pub/Sub Snapshot allows you to capture the state of a subscription at a given point in time and replay messages from that point. By using these features, you can ensure that the updated pipeline can process the messages that were delivered in the past two days without losing any data. References:
Pub/Sub Seek
Pub/Sub Snapshot

Cloud Bigtable is a sparsely populated table that can scale to billions of rows and thousands of columns, allowing you to store terabytes or even petabytes of data. A single value in each row is indexed; this value is known as the row key.
Reference: https://cloud.google.com/bigtable/docs/overview