neon/compute_tools/src/migration.rs

use anyhow::{Context, Result};
use fail::fail_point;
use postgres::Client;
use tracing::info;

/// Runs a series of migrations on a target database
pub(crate) struct MigrationRunner<'m> {
    client: &'m mut Client,
    migrations: &'m [&'m str],
}

impl<'m> MigrationRunner<'m> {
    /// Create a new migration runner
    pub fn new(client: &'m mut Client, migrations: &'m [&'m str]) -> Self {
        // The neon_migration.migration_id::id column is a bigint, which is equivalent to an i64
        assert!(migrations.len() + 1 < i64::MAX as usize);

        Self { client, migrations }
    }

    /// Get the current value neon_migration.migration_id
    fn get_migration_id(&mut self) -> Result<i64> {
        let query = "SELECT id FROM neon_migration.migration_id";
        let row = self
            .client
            .query_one(query, &[])
            .context("run_migrations get migration_id")?;

        Ok(row.get::<&str, i64>("id"))
    }

    /// Update the neon_migration.migration_id value
    ///
    /// This function has a fail point called compute-migration, which can be
    /// used if you would like to fail the application of a series of migrations
    /// at some point.
    fn update_migration_id(&mut self, migration_id: i64) -> Result<()> {
        // We use this fail point in order to check that failing in the
        // middle of applying a series of migrations fails in an expected
        // manner
        if cfg!(feature = "testing") {
            let fail = (|| {
                fail_point!("compute-migration", |fail_migration_id| {
                    migration_id == fail_migration_id.unwrap().parse::<i64>().unwrap()
                });

                false
            })();

            if fail {
                return Err(anyhow::anyhow!(format!(
                    "migration {} was configured to fail because of a failpoint",
                    migration_id
                )));
            }
        }

        self.client
            .query(
                "UPDATE neon_migration.migration_id SET id = $1",
                &[&migration_id],
            )
            .context("run_migrations update id")?;

        Ok(())
    }

    /// Prepare the migrations the target database for handling migrations
    fn prepare_database(&mut self) -> Result<()> {
        self.client
            .simple_query("CREATE SCHEMA IF NOT EXISTS neon_migration")?;
        self.client.simple_query("CREATE TABLE IF NOT EXISTS neon_migration.migration_id (key INT NOT NULL PRIMARY KEY, id bigint NOT NULL DEFAULT 0)")?;
        self.client.simple_query(
            "INSERT INTO neon_migration.migration_id VALUES (0, 0) ON CONFLICT DO NOTHING",
        )?;
        self.client
            .simple_query("ALTER SCHEMA neon_migration OWNER TO cloud_admin")?;
        self.client
            .simple_query("REVOKE ALL ON SCHEMA neon_migration FROM PUBLIC")?;

        Ok(())
    }

    /// Run the configrured set of migrations
    pub fn run_migrations(mut self) -> Result<()> {
        self.prepare_database()?;

        let mut current_migration = self.get_migration_id()? as usize;
        while current_migration < self.migrations.len() {
            macro_rules! migration_id {
                ($cm:expr) => {
                    ($cm + 1) as i64
                };
            }

            let migration = self.migrations[current_migration];

            if migration.starts_with("-- SKIP") {
                info!("Skipping migration id={}", migration_id!(current_migration));

                // Even though we are skipping the migration, updating the
                // migration ID should help keep logic easy to understand when
                // trying to understand the state of a cluster.
                self.update_migration_id(migration_id!(current_migration))?;
            } else {
                info!(
                    "Running migration id={}:\n{}\n",
                    migration_id!(current_migration),
                    migration
                );

                self.client
                    .simple_query("BEGIN")
                    .context("begin migration")?;

                self.client.simple_query(migration).with_context(|| {
                    format!(
                        "run_migrations migration id={}",
                        migration_id!(current_migration)
                    )
                })?;

                self.update_migration_id(migration_id!(current_migration))?;

                self.client
                    .simple_query("COMMIT")
                    .context("commit migration")?;

                info!("Finished migration id={}", migration_id!(current_migration));
            }

            current_migration += 1;
        }

        Ok(())
    }
}