Class: PgOnlineSchemaChange::Replay

Inherits:
Object
  • Object
show all
Extended by:
Helper
Defined in:
lib/pg_online_schema_change/replay.rb

Class Method Summary collapse

Methods included from Helper

logger, method_missing, primary_key, respond_to_missing?

Class Method Details

.begin! ⇒ Object

This, picks PULL_BATCH_COUNT rows by primary key from audit_table, replays it on the shadow_table. Once the batch is done, it them deletes those PULL_BATCH_COUNT rows from audit_table. Then, pull another batch, check if the row count matches PULL_BATCH_COUNT, if so swap, otherwise continue. Swap because, the row count is minimal to replay them altogether and perform the rename while holding an access exclusive lock for minimal time.



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# File 'lib/pg_online_schema_change/replay.rb', line 16

def begin!
  loop do
    rows = rows_to_play

    raise CountBelowDelta if rows.count <= client.delta_count

    play!(rows)
  end
end

.play!(rows, reuse_trasaction = false) ⇒ Object 



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# File 'lib/pg_online_schema_change/replay.rb', line 41

def play!(rows, reuse_trasaction = false)
  logger.info("Replaying rows, count: #{rows.size}")

  to_be_deleted_rows = []
  to_be_replayed = []
  rows.each do |row|
    new_row = row.dup

    # Remove audit table cols, since we will be
    # re-mapping them for inserts and updates
    reserved_columns.each do |col|
      new_row.delete(col)
    end

    if dropped_columns_list.any?
      dropped_columns_list.each do |dropped_column|
        new_row.delete(dropped_column)
      end
    end

    if renamed_columns_list.any?
      renamed_columns_list.each do |object|
        value = new_row.delete(object[:old_name])
        new_row[object[:new_name]] = value
      end
    end

    new_row = new_row.compact

    # quote indent column to preserve case insensitivity
    # ensure rows are escaped
    new_row = new_row.transform_keys do |column|
      client.connection.quote_ident(column)
    end

    new_row = new_row.transform_values do |value|
      client.connection.escape_string(value)
    end

    case row[operation_type_column]
    when "INSERT"
      values = new_row.map { |_, val| "'#{val}'" }.join(",")

      sql = <<~SQL
        INSERT INTO #{shadow_table} (#{new_row.keys.join(",")})
          VALUES (#{values});
      SQL
      to_be_replayed << sql

      to_be_deleted_rows << "'#{row[audit_table_pk]}'"
    when "UPDATE"
      set_values = new_row.map do |column, value|
        "#{column} = '#{value}'"
      end.join(",")

      sql = <<~SQL
        UPDATE #{shadow_table}
        SET #{set_values}
        WHERE #{primary_key}=\'#{row[primary_key]}\';
      SQL
      to_be_replayed << sql

      to_be_deleted_rows << "'#{row[audit_table_pk]}'"
    when "DELETE"
      sql = <<~SQL
        DELETE FROM #{shadow_table} WHERE #{primary_key}=\'#{row[primary_key]}\';
      SQL
      to_be_replayed << sql

      to_be_deleted_rows << "'#{row[audit_table_pk]}'"
    end
  end

  Query.run(client.connection, to_be_replayed.join, reuse_trasaction)

  # Delete items from the audit now that are replayed
  return unless to_be_deleted_rows.count >= 1

  delete_query = <<~SQL
    DELETE FROM #{audit_table} WHERE #{audit_table_pk} IN (#{to_be_deleted_rows.join(",")})
  SQL
  Query.run(client.connection, delete_query, reuse_trasaction)
end

.reserved_columns ⇒ Object 



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# File 'lib/pg_online_schema_change/replay.rb', line 37

def reserved_columns
  @reserved_columns ||= [trigger_time_column, operation_type_column, audit_table_pk]
end

.rows_to_play(reuse_trasaction = false) ⇒ Object 



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# File 'lib/pg_online_schema_change/replay.rb', line 26

def rows_to_play(reuse_trasaction = false)
  select_query = <<~SQL
    SELECT * FROM #{audit_table} ORDER BY #{audit_table_pk} LIMIT #{client.pull_batch_count};
  SQL

  rows = []
  Query.run(client.connection, select_query, reuse_trasaction) { |result| rows = result.map { |row| row } }

  rows
end