Merge bitcoin/bitcoin#26471: Reduce default mempool size in -blocksonly mode

8e85164e7d12be324ea1af2e288ebcf689c930b7 doc: release note on mempool size in -blocksonly (willcl-ark)
ae797463dc7c72d990afa3ca53eeced7563ccd29 doc: Update blocksonly behaviour in reduce-memory (willcl-ark)
1134686ef92fb622ac32dc7463d3763cf18c85ad mempool: Don't share mempool with dbcache in blocksonly (willcl-ark)

Pull request description:

  Fixes #9526

  When `-blocksonly` has been set reduce default mempool size to avoid surprising resource usage via sharing un-used mempool cache space with dbcache.

  In comparison to https://github.com/bitcoin/bitcoin/pull/9569 which either set `maxmempool` size to 0 when `-blocksonly` was set or else errored on startup, this change will permit `maxmempool` options being set.

  This preserves the current (surprising?) behaviour of having a functional mempool in `-blocksonly` mode, to permit whitelisted peer transaction relay, whilst reducing average runtime memory usage for blocksonly nodes which either use the default settings or have otherwise configured a `maxmempool` size.

  To use the previous old defaults node operators can configure their node with: `-blocksonly -maxmempool=300`.

ACKs for top commit:
  ajtowns:
    ACK 8e85164e7d12be324ea1af2e288ebcf689c930b7
  stickies-v:
    re-ACK https://github.com/bitcoin/bitcoin/commit/8e85164e7d12be324ea1af2e288ebcf689c930b7

Tree-SHA512: 1c461c24b6f14ba02cfe4e2cde60dc629e47485db5701bca3003b8df79e3aa311c0c967979f6a1dca3ba69f5b1e45fa2db6ff83352fdf2d4349d5f8d120e740d

0 files changed, 0 insertions, 0 deletions