Optimise TrieLogPruner.preload

[siladu]

These optimisations only seem to save <= 17% of the time.

Control node took ~6mins.
Test node took between 5 mins and 5 mins 30 seconds on a couple of runs.

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The problem with #7337 is that for the duration of the async load, block import time appears to be affected. This could lead to impaired attestation performance and a missed proposal (although admittedly better than the alternative of downtime).

Ultimately need another PR that used a reasonable timeout for this load+prune operation, maybe 30 seconds.

[siladu]

Wall clock profiling of

• control - dev-clc-bu-tk-mainnet-mainnet-archive-simon-test-snapshot4
• test - dev-clc-bu-tk-mainnet-mainnet-archive-simon-test-snapshot5

besu_7350_wallclock.tar.gz

[ahamlat]

The parallelization didn't work very well. For example , the main thread didn't execute any of the tasks, it was just waiting for the other threads from ForkjoinPool.commonPool, which is not the expected behaviour. The main thread with (numCPU - 1) other threads from ForkjoinPool.commonPool should do the work in a proportional way.
In the profiling, in addition to the main thread, I see also that all the ForkjoinPool.commonPool threads are not used, ex [ForkJoinPool.commonPool-worker-2 tid=37631].
The iterator could be the issue, I think you need to review the way you access database, you don't need RocksDB iterator if you can all the keys.

[siladu]

Superceded by #7365