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Replace hardcoded WithGlobalLock assignment with configurable options wallet postgres backends. Also add the WithGlobalLock option to the channeldb table for postgres backends. Defaults: - channeldb: false (allow concurrent access) - wallet: true (maintain safe single-writer behavior) Users can now override these defaults via: - db.postgres.channeldb-with-global-lock - db.postgres.walletdb-with-global-lock This gives operators flexibility while maintaining safe defaults until full native SQL migration is complete. Moreover exclude db.postgres.walletdb-with-global-lock check in the sample config file script. We cannot easily check the correct default because we set it later in the LND startup sequence so we exclude it.
77 lines
3.1 KiB
Markdown
77 lines
3.1 KiB
Markdown
# Postgres support in LND
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With the introduction of the `kvdb` interface, LND can support multiple database
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backends. One of the supported backends is Postgres. This document
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describes how it can be configured.
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## Building LND with postgres support
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Since `lnd v0.14.1-beta` the necessary build tags to enable postgres support are
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already enabled by default. The default release binaries or docker images can
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be used. To build from source, simply run:
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```shell
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$ make install
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```
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## Configuring Postgres for LND
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In order for LND to run on Postgres, an empty database should already exist. A
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database can be created via the usual ways (psql, pgadmin, etc.). A user with
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access to this database is also required.
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Creation of a schema and the tables is handled by LND automatically.
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## Configuring LND for Postgres
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LND is configured for Postgres through the following configuration options:
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* `db.backend=postgres` to select the Postgres backend.
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* `db.postgres.dsn=...` to set the database connection string that includes
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database, user and password.
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* `db.postgres.timeout=...` to set the connection timeout. If not set, no
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timeout applies.
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Example as follows:
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```
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[db]
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db.backend=postgres
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db.postgres.dsn=postgresql://dbuser:dbpass@127.0.0.1:5432/dbname
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db.postgres.timeout=0
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```
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Connection timeout is disabled, to account for situations where the database
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might be slow for unexpected reasons.
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Moreover for particular kv tables we also add the option to access the
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tables via a global lock (single wirter). This is a temorpary measure until
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these particular tables have a native sql schema. This helps to mitigate
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resource exhaustion in case LND experiencing high concurrent load:
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* `db.postgres.walletdb-with-global-lock=true` to run LND with a single writer
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for the walletdb_kv table (default is true).
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* `db.postgres.channeldb-with-global-lock=false` to run the channeldb_kv table
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with a single writer (default is false).
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## Important note about replication
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In case a replication architecture is planned, streaming replication should be avoided, as the master does not verify the replica is indeed identical, but it will only forward the edits queue, and let the slave catch up autonomously; synchronous mode, albeit slower, is paramount for `lnd` data integrity across the copies, as it will finalize writes only after the slave confirmed successful replication.
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## What is in the database?
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At present, the Postgres Database functions as a Key-Value Store, much as Bolt DB does. Some values are TLV-encoded while others are not. More schema will be introduced over time. At present the schema for each table/relation is simply: `key`, `value`, `parent_id`, `id`, `sequence`.
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List of tables/relations:
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```
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List of relations
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Schema | Name | Type | Owner
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--------+------------------+-------+----------
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public | channeldb_kv | table | lndadmin
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public | decayedlogdb_kv | table | lndadmin
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public | macaroondb_kv | table | lndadmin
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public | towerclientdb_kv | table | lndadmin
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public | towerserverdb_kv | table | lndadmin
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public | walletdb_kv | table | lndadmin
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```
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Notably, Invoice DB is maintained separately alongside the LND node.
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