[Enhancement]: Abandon the time travel feature

[jiaoew1991]

Is there an existing issue for this?

• I have searched the existing issues

What would you like to be added?

In the early versions, Milvus added the time travel feature. However, it did not achieve the expected results in terms of community feedback and actual effectiveness. Instead, it introduced many obstacles to stability and other feature designs. For example, when designing functions such as TTL, compaction, and garbage collection, compatibility with time travel must be considered, resulting in significant complexity.

Considering the reasons mentioned above, it is recommended to remove the time travel feature in version 2.3.0 upgrade.

Why is this needed?

No response

Anything else?

No response

[jiaoew1991]

We should follow the following steps to execute:

• Deprecated the time travel parameter in Milvus interface, remove related implementations and test cases internally Remove time travel 1 #26119
• Remove relevant introductions from the documentation
• Remove time travel support from PyMilvus Remove time travel params pymilvus#1635
• Remove time travel support from Go SDK Remove time travel milvus-sdk-go#549
• Remove time travel support from Java SDK

[xiaofan-luan]

Agreed.
Remove timetravel can improve the search performance by

1. pre calculate delete bitset
2. sort the data by pk instead of timestamp and save pk index.

and maybe more ....

[jiaoew1991]

The current handling of search and query for travel_ts is different.

1. If the user does not set travel_ts, search will use max_ts. Previously, we attempted to change the default value to the query time, but it had a significant impact on the merging of search tasks because the merging conditions include whether the travel_ts of two search tasks are equal. Therefore, the current search does not guarantee mvcc.

2. If the user does not set travel_ts in a query, proxy will use the query time, which ensures mvcc.

We can delete all travel_ts on the search path because consistency is not necessary for search, and performance is more important. However, the travel_ts of the query needs to be retained but renamed as mvcc. Consistency is necessary for subsequent scenarios such as deduplication of primary keys and delete by expr where querying is done before writing.

[jiaoew1991]

finished it