Handle deleted projections tables while triggering projections

[the-mikedavis]

The test case in this change shows an example that can cause an error log. One client of Khepri sends an unregister_projections command while another sends many changes which affect a projection which is being unregistered. Using async commands makes the error much more likely to occur.

Ra applies committed commands in a batch and then handles all effects created by the batch. In this scenario the unregister_projections command may end up being applied by Ra in a batch with the async commands and the resulting effects list will contain aux effects to trigger projections (casued by the async commands) and an aux effect to unregister the projection. Some trigger aux effects may come later in the list than the unregister_projections effect and so their projection table will be deleted. In this case we want to perform a no-op for the trigger effect.

We already no-op these effects because we wrap ETS calls in try expressions. This change avoids an error log caused by ETS calls attempting to insert or delete records in an undefined table.

Example error log...

This is from the commontest output of the added test case before the fix in khepri_projection.erl:

2024-09-10T09:48:20.686591-04:00 <0.173.0>: Failed to insert record into ETS table for projection: cluster_SUITE
  Record:
    {[key],116}
  Crash:
    exception error: bad argument
     in function  ets:insert/2
        called as ets:insert(undefined,{[key],116})
        *** argument 1: the table identifier does not refer to an existing ETS table
     in call from khepri_projection:try_ets_insert/3 (/nix/persist/home/michael/src/rabbitmq/khepri/src/khepri_projection.erl, line 446)
     in call from khepri_projection:trigger_simple_projection/6 (/nix/persist/home/michael/src/rabbitmq/khepri/src/khepri_projection.erl, line 405)
     in call from khepri_machine:handle_aux/6 (/nix/persist/home/michael/src/rabbitmq/khepri/src/khepri_machine.erl, line 1242)
     in call from ra_server:handle_aux/4 (/nix/persist/home/michael/src/rabbitmq/khepri/_build/default/lib/ra/src/ra_server.erl, line 1632)
     in call from ra_server_proc:handle_effect/5 (/nix/persist/home/michael/src/rabbitmq/khepri/_build/default/lib/ra/src/ra_server_proc.erl, line 1394)
     in call from lists:foldl_1/3 (lists.erl, line 1599)
     in call from ra_server_proc:handle_effects/5 (/nix/persist/home/michael/src/rabbitmq/khepri/_build/default/lib/ra/src/ra_server_proc.erl, line 1301)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.68%. Comparing base (e31b236) to head (cead845).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #293      +/-   ##
==========================================
+ Coverage   89.64%   89.68%   +0.03%     
==========================================
  Files          21       21              
  Lines        3187     3188       +1     
==========================================
+ Hits         2857     2859       +2     
+ Misses        330      329       -1     

Flag	Coverage Δ
erlang-25	88.92% <100.00%> (+0.03%)	⬆️
erlang-26	89.49% <100.00%> (-0.03%)	⬇️
erlang-27	89.61% <100.00%> (+0.09%)	⬆️
os-ubuntu-latest	89.68% <100.00%> (+0.03%)	⬆️
os-windows-latest	89.55% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.