Add replace member changes. Perist membership details.

[sanebay]

No description provided.

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 21.81818% with 43 lines in your changes missing coverage. Please review.

Project coverage is 65.18%. Comparing base (acb04e8) to head (68eb07d).
Report is 23 commits behind head on main.

Files with missing lines	Patch %	Lines
src/lib/homestore_backend/hs_pg_manager.cpp	7.31%	37 Missing and 1 partial ⚠️
...ib/homestore_backend/replication_state_machine.cpp	0.00%	2 Missing ⚠️
src/include/homeobject/pg_manager.hpp	50.00%	1 Missing ⚠️
src/lib/homestore_backend/hs_blob_manager.cpp	0.00%	1 Missing ⚠️
src/lib/memory_backend/mem_pg_manager.cpp	83.33%	0 Missing and 1 partial ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##             main     #216      +/-   ##
==========================================
- Coverage   68.69%   65.18%   -3.52%     
==========================================
  Files          30       32       +2     
  Lines        1581     1772     +191     
  Branches      163      191      +28     
==========================================
+ Hits         1086     1155      +69     
- Misses        408      522     +114     
- Partials       87       95       +8     

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[xiaoxichen]

+1 from my side and waiting for the testing result

[xiaoxichen]

As discussed in the meeting, we need to re-think the flow with the learner changes. My feeling is we need to wait till the learner flip to follower (voter) then do the step 3

// Step 3. Append log entry to mark the old member is out and new member is added.

and setp 4

            // Step 4. Remove the old member. Even if the old member is temporarily
            // down and recovers, nuraft mesg see member remove from cluster log
            // entry and call exit_group() and leave().

Likely we need to hook up to the

void RaftStateMachine::commit_config

to get notification on cluster member change especially learner flipped to follower.

[xiaoxichen]

Please if you can rebase.

[xiaoxichen]

HomeObject struct pg_members is identical to homestore::replica_member_info as of now.

As homestore::replica_member_info is the only information that follower can get regarding a PG, I doubt there is a possibility HomeObject::pg_members can diverse from homestore::replica_member_info

Thinking about consolidate them together, not blocking, more for discussion

fixed

[sanebay]

As discussed in the meeting, we need to re-think the flow with the learner changes. My feeling is we need to wait till the learner flip to follower (voter) then do the step 3
why should we wait ? why not treat as normal follower ?

[xiaoxichen]

why should we wait ? why not treat as normal follower ?

I think it is same when the out_member has down. But if the out_member is healthy , i.e PG move for balancing/tech refresh etc, keeping the redundancy has advantage. If we dont wait till new_member catch up before deleting out_member, we made us degrade to 2 replica.

[xiaoxichen]

lgtm

[sanebay]

why should we wait ? why not treat as normal follower ?

I think it is same when the out_member has down. But if the out_member is healthy , i.e PG move for balancing/tech refresh etc, keeping the redundancy has advantage. If we dont wait till new_member catch up before deleting out_member, we made us degrade to 2 replica.

Created a story for this. eBay/HomeStore#573 This has to be optional depending on use case. Sometimes, its better to evict immediately to free up space.

[xiaoxichen]

feel free to merge and as you said that can track by other ticket.