docs: Document additional config settings

[xrpl365]

Summary

The server reads a number of configuration settings that the shipped example
config (cfg/xrpld-example.cfg) and cfg/validators-example.txt never mention,
so operators can only discover them by reading the source. This PR adds
commented-out documentation for the operator-facing ones, with every value,
default, and constraint verified against the parsing code.

Everything added is commented out, so there is no behavior change.

How these were found

Rather than work from the existing docs, each setting was found by enumerating
every config read-site in src/xrpld and src/libxrpl (section(...),
valueOr/value_or, exists, get/getIfExists/get<T>, set(...),
getSingleSection, legacy, and operator[], resolving the section and key
constants in include/xrpl/config/Constants.h) and diffing that set against
everything documented in the two shipped files. Read-sites in src/test were
excluded, so every setting below is read by production code. Defaults and
constraints were then read directly from the source lines cited in the table.

Changes

cfg/xrpld-example.cfg

Peer Protocol:

• [peers_in_max] / [peers_out_max]: inbound/outbound peer connection
  limits. Must be set together; ignored if the legacy [peers_max] is set.
• [network_quorum]: minimum connected peers before joining consensus
  (default 1; not the UNL/validation quorum).
• [reduce_relay]: bandwidth-reduction options: vp_base_squelch_enable
  (default off), vp_base_squelch_max_selected_peers (5), tx_enable (off),
  tx_min_peers (20), tx_relay_percentage (25), tx_metrics (off). The
  older vp_enable is documented as a deprecated alias.
• [hashrouter]: hold_time (default 300s, min 12) and relay_time
  (default 30s, min 8, must not exceed hold_time) for duplicate-message
  suppression/relay.

Database:

• [ledger_tx_tables] use_tx_tables: default 1; 0 disables the SQLite
  transaction index tables, after which tx, account_tx, and tx_history
  return notEnabled. Does not stop transactions being stored in ledgers.
• [node_db] RocksDB-only tuning keys: cache_mb, open_files,
  file_size_mb, file_size_mult, bg_threads, high_threads, hard_set
  (documented as optional; the server otherwise sizes them from [node_size]).
• [sqdb] backend: selects the relational-database backend; only sqlite
  is supported (and is the default).

Voting / amendments:

• [amendments] / [veto_amendments]: amendments this server votes for or
  against. Each line is a 64-char hex amendment ID followed by its name.
• [amendment_majority_time]: how long an amendment must hold majority before
  activation (default 2 weeks, min 15 minutes).
• [features]: force-enables features in locally-built ledgers. Documented
  with a clear note that it is for standalone/testing only and can cause a
  networked server to lose sync or stop processing (downtime).

Misc:

• [sweep_interval]: cache sweep interval in seconds (10 to 600; derived from
  [node_size] when unset).
• [elb_support]: default 0; gates serverOkay() load-balancer health
  reporting.

cfg/validators-example.txt

• [validator_keys]: an additional list of validator public keys, merged with
  [validators] at startup (kept for backward compatibility). Documented
  alongside its sibling validator sections.

How to verify

Setting	Default / constraint	Source of truth
peers_in_max / peers_out_max	max 1000 / 10 to 1000; must pair	src/xrpld/core/detail/Config.cpp:547-577
network_quorum	default 1	src/xrpld/core/detail/Config.cpp:676
reduce_relay keys	off / 5 / off / 20 / 25 / off	src/xrpld/core/detail/Config.cpp:794-861
vp_enable deprecated	error if set with vp_base_squelch_enable	src/xrpld/core/detail/Config.cpp:801-813
hashrouter hold/relay	300s (min 12) / 30s (min 8, at most hold_time)	src/xrpld/app/misc/detail/setup_HashRouter.cpp:26-48; defaults include/xrpl/core/HashRouter.h:112,117
use_tx_tables	default true	src/xrpld/core/detail/Config.cpp:413-414; gated in src/xrpld/app/rdb/backend/detail/SQLiteDatabase.cpp
node_db RocksDB keys	optional; node-size derived if unset	src/libxrpl/nodestore/backend/RocksDBFactory.cpp:117-170
sqdb backend	default sqlite; only sqlite accepted	src/libxrpl/rdb/SociDB.cpp:55-59
amendments / veto_amendments	hex ID + name per line	src/xrpld/app/main/Application.cpp:1245-1247; parse src/xrpld/app/misc/detail/AmendmentTable.cpp:50-80
amendment_majority_time	default 2 weeks, min 15 min	src/xrpld/core/detail/Config.cpp:959-993; default include/xrpl/protocol/SystemParameters.h:81
features	feature names; standalone/test	src/xrpld/core/detail/Config.cpp:1164-1176
sweep_interval	10 to 600s; node-size derived	src/xrpld/core/detail/Config.cpp:740-747; use src/xrpld/app/main/Application.cpp:929-931
elb_support	default 0	src/xrpld/app/main/Application.cpp:2106
validator_keys	merged into [validators]	src/xrpld/core/detail/Config.cpp:1080-1153

Notes for reviewers

• Some advanced RocksDB configs that are read but unlikely to be useful to most
  operators (the raw options/bbt_options strings, filter_bits,
  filter_full, block_size, universal_compaction, and rq_bundle) were
  intentionally left undocumented to keep the example file focused. They can be
  added on request.

Type of change

docs: documentation only, no functional change.

[Copilot]

🟡 Changes recommended

The new [elb_support] documentation omits an availability condition actually enforced by serverOkay() (“Too much load”), so the operator-facing description is incomplete.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

This PR updates the shipped example configuration files to document additional operator-facing settings that are already parsed/used by the server but previously undocumented in cfg/xrpld-example.cfg and cfg/validators-example.txt, with no behavioral changes (all additions are commented).

Changes:

• Documents peer/overlay-related settings including [peers_in_max], [peers_out_max], [network_quorum], [reduce_relay], and [hashrouter].
• Documents additional database-related settings including [ledger_tx_tables] / use_tx_tables, RocksDB tuning keys under [node_db], and [sqdb] backend.
• Documents amendment/feature-related settings and adds [validator_keys] documentation in the validators example file.

File summaries

File	Description
cfg/xrpld-example.cfg	Adds commented documentation for several previously-undocumented config sections/keys (peering, relay/hashrouter tuning, DB toggles/tuning, amendments/features, misc).
cfg/validators-example.txt	Adds commented documentation for the [validator_keys] section and how it is merged/used at startup.

Review details

• Files reviewed: 2/2 changed files
• Comments generated: 1
• Review effort level: Lite

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