lhotari commented on PR #24623:
URL: https://github.com/apache/pulsar/pull/24623#issuecomment-3208984303

   Interestingly, the results on my Dell XPS 2019 (i9-9980HK CPU @ 2.40GHz) are 
very different than on MBP M3 Max:
   
   ```
   
┌────────────────────────────────────┬──────────┬──────────┬───────────┬──────────┬─────────────────┬────────┬────────┬──────────┬─────────────────────────┐
   │            description             │ produced │ consumed │ consumers │ 
bk_reads │ bk_read_entries │  hits  │ misses │ restarts │           ts          
  │
   │              varchar               │  int64   │  int64   │   int64   │  
int64   │      int64      │ double │ double │  int64   │        timestamp       
 │
   
├────────────────────────────────────┼──────────┼──────────┼───────────┼──────────┼─────────────────┼────────┼────────┼──────────┼─────────────────────────┤
   │ PR12258                            │  1509385 │ 15098443 │        10 │    
18525 │         1847641 │  87.76 │  12.24 │        3 │ 2025-08-20 19:35:26.07  │
   │ PR12258                            │  1693476 │ 16940269 │        10 │    
13736 │         1368859 │  91.92 │   8.08 │        3 │ 2025-08-20 19:36:00.442 │
   │ PR12258                            │  1723156 │ 17237529 │        10 │    
12683 │         1262572 │  92.68 │   7.32 │        3 │ 2025-08-20 19:36:34.506 │
   │ PR12258                            │  1719958 │ 17205041 │        10 │    
13614 │         1354546 │  92.13 │   7.87 │        3 │ 2025-08-20 19:37:08.873 │
   │ PR12258                            │  1644804 │ 16454401 │        10 │    
11411 │         1136525 │  93.09 │   6.91 │        3 │ 2025-08-20 19:37:43.28  │
   │ cacheEvictionByMarkDeletedPosition │  1859918 │ 18607060 │        10 │    
81565 │         8129842 │  56.31 │  43.69 │        3 │ 2025-08-20 19:38:27.66  │
   │ cacheEvictionByMarkDeletedPosition │  1814244 │ 18145240 │        10 │    
81722 │         8131713 │  55.19 │  44.81 │        3 │ 2025-08-20 19:39:01.718 │
   │ cacheEvictionByMarkDeletedPosition │  1740813 │ 17412731 │        10 │    
60897 │         6042479 │   65.3 │   34.7 │        3 │ 2025-08-20 19:39:35.845 │
   │ cacheEvictionByMarkDeletedPosition │  1664006 │ 16644406 │        10 │    
38717 │         3863385 │  76.79 │  23.21 │        3 │ 2025-08-20 19:40:09.946 │
   │ cacheEvictionByMarkDeletedPosition │  1758310 │ 17593905 │        10 │    
77274 │         7686870 │  56.31 │  43.69 │        3 │ 2025-08-20 19:40:43.946 │
   │ PIP430                             │  1826902 │ 18272962 │        10 │    
14760 │         1471620 │  91.95 │   8.05 │        3 │ 2025-08-20 19:41:28.689 │
   │ PIP430                             │  1721983 │ 17226790 │        10 │     
8366 │          835071 │  95.15 │   4.85 │        3 │ 2025-08-20 19:42:03.198 │
   │ PIP430                             │  1711848 │ 17137830 │        10 │     
1985 │          197240 │  98.85 │   1.15 │        3 │ 2025-08-20 19:42:37.248 │
   │ PIP430                             │  1710176 │ 17111540 │        10 │     
4288 │          428004 │   97.5 │    2.5 │        3 │ 2025-08-20 19:43:11.528 │
   │ PIP430                             │  1690152 │ 16912942 │        10 │     
1937 │          192703 │  98.86 │   1.14 │        3 │ 2025-08-20 19:43:45.748 │
   │ PIP430disabled                     │  1872724 │ 18734102 │        10 │    
78763 │         7842919 │  58.14 │  41.86 │        3 │ 2025-08-20 19:44:30.079 │
   │ PIP430disabled                     │  1793152 │ 17940620 │        10 │    
79898 │         7936811 │  55.76 │  44.24 │        3 │ 2025-08-20 19:45:04.486 │
   │ PIP430disabled                     │  1755762 │ 17563500 │        10 │    
77663 │         7726275 │  56.01 │  43.99 │        3 │ 2025-08-20 19:45:38.471 │
   │ PIP430disabled                     │  1773824 │ 17743593 │        10 │    
78873 │         7846181 │  55.78 │  44.22 │        3 │ 2025-08-20 19:46:12.815 │
   │ PIP430disabled                     │  1683544 │ 16839721 │        10 │    
49009 │         4875186 │  71.05 │  28.95 │        3 │ 2025-08-20 19:46:47.135 │
   
├────────────────────────────────────┴──────────┴──────────┴───────────┴──────────┴─────────────────┴────────┴────────┴──────────┴─────────────────────────┤
   │ 20 rows                                                                    
                                                                   10 columns │
   
└──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
   ```
   
   What seems to happen is that when CPU resources are scarce, differences in 
caching efficiency will accumulate, as the additional overhead from cache 
misses creates bottlenecks that propagate through the system, causing small 
efficiency gaps to manifest as significant performance differences under 
sustained load.
   
   The test case uses a PulsarMockBookKeeper, so storage operations themselves 
are fast. The test case doesn't add a penalty for reads at the moment. In 
reality, each read would occur more latency. This isn't a fully realistic test 
case, but it does show that PIP430 caching strategy is superior over others for 
the rolling restarts use case.
   
   One of the gaps of the test case is that it currently doesn't have a 
constraint on caching since there's no other active topics that would be 
filling the cache and causing it to overflow. A test where this happens would 
be useful since it could demonstrate the PIP430 strategy for handling cache 
overflowing.


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