Configure stellar-core to use SQLite instead of PostgreSQL

[leighmcculloch]

What

Switch stellar-core's database from PostgreSQL to SQLite by default across all network configurations (local, testnet, pubnet, futurenet). PostgreSQL support is retained for backwards compatibility via the CORE_USE_POSTGRES=true environment variable.

Why

With RPC becoming more prevalent as the primary interface (vs Horizon), there may be scenarios where users run stellar-core and RPC instead of stellar-core, Horizon, and RPC - in which case PostgreSQL would be running solely for core's database.

Changes

• SQLite is now the default database for stellar-core
• PostgreSQL can still be used by setting CORE_USE_POSTGRES=true
• PostgreSQL support for stellar-core in Quickstart is deprecated and may be removed in a future release
• PostgreSQL is only started when Horizon is enabled OR when CORE_USE_POSTGRES=true

Close #875

Todo

• Get feedback from @mollykarcher @johncanneto on Configuring stellar-core to use SQLite instead of PostgreSQL #875 (comment)
• Get feedback from anyone else in https://stellarfoundation.slack.com/archives/C9H5JTW1J/p1767848039928449

[Copilot]

Pull request overview

This PR migrates stellar-core from using PostgreSQL to SQLite across all network configurations (testnet, pubnet, local, futurenet). The changes remove the core database creation from PostgreSQL initialization and ensure PostgreSQL only starts when Horizon is enabled. Documentation is updated to reflect that PostgreSQL is now exclusively for Horizon data.

Key Changes

• Stellar-core configurations now use SQLite at /opt/stellar/core/stellar.db instead of PostgreSQL
• PostgreSQL database initialization only runs when Horizon is enabled
• Removed core database creation and related grants from PostgreSQL setup
• Updated README to document that PostgreSQL is only for Horizon data

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
testnet/core/etc/stellar-core.cfg	Changed DATABASE from PostgreSQL to SQLite
pubnet/core/etc/stellar-core.cfg	Changed DATABASE from PostgreSQL to SQLite
local/core/etc/stellar-core.cfg	Changed DATABASE from PostgreSQL to SQLite and removed commented alternatives
futurenet/core/etc/stellar-core.cfg	Changed DATABASE from PostgreSQL to SQLite
start	Updated init_db to only run for Horizon, removed core database creation, removed PostgreSQL dependencies from stellar-core initialization and startup
README.md	Updated documentation to reflect PostgreSQL is only for Horizon; added note about historical PostgreSQL usage for stellar-core

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[leighmcculloch]

Testing side-by-side with the latest stellar/quickstart image in --local mode, this change using sqlite reduces startup time by 4-5s, and memory usage by 40-50mb.

[leighmcculloch]

Updated the PR to retain PostgreSQL support for backwards compatibility. SQLite is now the default, but PostgreSQL can still be used by setting CORE_USE_POSTGRES=true.

PostgreSQL support for stellar-core in Quickstart is marked as deprecated and may be removed in a future release. If you're currently using PostgreSQL for stellar-core, please comment on #875 with information about your use case.