tasks/common/persistence/sql/sqlplugin/postgres/cluster_metadata.go

// Copyright (c) 2020 Temporal Technologies, Inc.
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package postgres

import (
	"database/sql"

	"github.com/temporalio/temporal/common/persistence/sql/sqlplugin"
)

const constMetadataPartition = 0
const (
	// One time only for the immutable data, so just use idempotent insert that does nothing if a record exists
	// This particular query requires PostgreSQL 9.5, PostgreSQL 9.4 comes out of LTS on February 13, 2020
	// QueryInfo: https://wiki.postgresql.org/wiki/What%27s_new_in_PostgreSQL_9.5#INSERT_..._ON_CONFLICT_DO_NOTHING.2FUPDATE_.28.22UPSERT.22.29
	insertClusterMetadataOneTimeOnlyQry = `INSERT INTO 
cluster_metadata (metadata_partition, immutable_data, immutable_data_encoding)
VALUES($1, $2, $3)
ON CONFLICT DO NOTHING`

	getImmutableClusterMetadataQry = `SELECT immutable_data, immutable_data_encoding FROM 
cluster_metadata WHERE metadata_partition = $1`
)

// Does not follow traditional lock, select, read, insert as we only expect a single row.
func (pdb *db) InsertIfNotExistsIntoClusterMetadata(row *sqlplugin.ClusterMetadataRow) (sql.Result, error) {
	return pdb.conn.Exec(insertClusterMetadataOneTimeOnlyQry,
		constMetadataPartition,
		row.ImmutableData,
		row.ImmutableDataEncoding)
}

func (pdb *db) GetClusterMetadata() (*sqlplugin.ClusterMetadataRow, error) {
	var row sqlplugin.ClusterMetadataRow
	err := pdb.conn.Get(&row, getImmutableClusterMetadataQry, constMetadataPartition)
	if err != nil {
		return nil, err
	}
	return &row, err
}