PostgreSQL: fix ActiveRecord.default_timezone runtime switching being ignored

lib/arjdbc/postgresql/adapter.rb

@@ -69,6 +69,12 @@ def set_client_encoding(encoding)
     # Configures the encoding, verbosity, schema search path, and time zone of the connection.
     # This is called on `connection.connect` and should not be called manually.
     def configure_connection
+      # Record the zone state first: the statements below re-enter
+      # #internal_exec_query -> #update_typemap_for_default_timezone.
+      # (Not @default_timezone: Rails treats that as a per-connection override.)
+      @configured_default_timezone = ActiveRecord.default_timezone
+      @configured_local_tz = @configured_default_timezone == :local ? local_tz : nil
+
       #if encoding = config[:encoding]
         # The client_encoding setting is set by the driver and should not be altered.
         # If the driver detects a change it will abort the connection.
@@ -532,6 +538,13 @@ def execute_batch(statements, name = nil)
       execute(combine_multi_statements(statements), name)
     end
 
+    # ActiveRecord's query path goes through internal_exec_query, not
+    # exec_no_cache/exec_cache, so pick up default_timezone changes here.
+    def internal_exec_query(...)
+      update_typemap_for_default_timezone
+      super
+    end
+
     # from ActiveRecord::ConnectionAdapters::PostgreSQL::DatabaseStatements
     READ_QUERY = ActiveRecord::ConnectionAdapters::AbstractAdapter.build_read_query_regexp(
       :close, :declare, :fetch, :move, :set, :show
@@ -794,7 +807,8 @@ def extract_pg_identifier_from_name(name)
     end
 
     def local_tz
-      @local_tz ||= execute('SHOW TIME ZONE', 'SCHEMA').first["TimeZone"]
+      # not memoized: the process zone can change at runtime (ENV['TZ'] / Java default)
+      java.util.TimeZone.getDefault.getID
     end
 
     def bind_params_length

lib/arjdbc/postgresql/oid_types.rb

@@ -231,21 +231,14 @@ def load_types_queries(initializer, oids)
         end
       end
 
+      # The JDBC driver returns timestamps in the session time zone set by
+      # #configure_connection, so when ActiveRecord.default_timezone (or the
+      # process zone, while :local) changes at runtime, re-run it.
       def update_typemap_for_default_timezone
-        if @default_timezone != ActiveRecord.default_timezone && @timestamp_decoder
-          decoder_class = ActiveRecord.default_timezone == :utc ?
-                            PG::TextDecoder::TimestampUtc :
-                            PG::TextDecoder::TimestampWithoutTimeZone
+        local = ActiveRecord.default_timezone == :local ? local_tz : nil
+        return if @configured_default_timezone == ActiveRecord.default_timezone && @configured_local_tz == local
 
-          @timestamp_decoder = decoder_class.new(@timestamp_decoder.to_h)
-          @connection.type_map_for_results.add_coder(@timestamp_decoder)
-
-          @default_timezone = ActiveRecord.default_timezone
-
-          # if default timezone has changed, we need to reconfigure the connection
-          # (specifically, the session time zone)
-          configure_connection
-        end
+        configure_connection if @raw_connection
       end
 
       def extract_scale(sql_type)

src/java/arjdbc/postgresql/PostgreSQLRubyJdbcConnection.java

@@ -347,7 +347,7 @@ protected void setTimestampParameter(final ThreadContext context,
         final int index, IRubyObject value,
         final IRubyObject attribute, final int type) throws SQLException {
         // PGJDBC uses strings internally anyway, so using Timestamp doesn't do any good
-        String tsString = PgDateTimeUtils.timestampValueToString(context, value, null, true);
+        String tsString = PgDateTimeUtils.timestampValueToString(context, value, getDefaultTimeZone(context), true);
         statement.setObject(index, tsString, Types.OTHER);
     }
 

test/db/postgresql/default_timezone_test.rb

@@ -0,0 +1,42 @@
+require 'test_helper'
+require 'db/postgres'
+
+class PostgresDefaultTimezoneTest < Test::Unit::TestCase
+
+  def setup
+    @orig_tz = java.util.TimeZone.getDefault
+    @orig_default = ActiveRecord.default_timezone
+  end
+
+  def teardown
+    java.util.TimeZone.setDefault(@orig_tz)
+    ActiveRecord.default_timezone = @orig_default
+    connection.select_value('SELECT 1') # re-sync session zone
+  end
+
+  def test_session_zone_follows_default_timezone_at_runtime
+    ActiveRecord.default_timezone = :utc
+    assert_equal 'UTC', session_zone
+
+    ActiveRecord.default_timezone = :local
+    set_process_zone 'Asia/Tokyo'
+    assert_equal 'Asia/Tokyo', session_zone
+
+    # symbol stays :local, only the zone changes
+    set_process_zone 'America/New_York'
+    assert_equal 'America/New_York', session_zone
+
+    ActiveRecord.default_timezone = :utc
+    assert_equal 'UTC', session_zone
+  end
+
+  private
+
+  def connection; ActiveRecord::Base.connection; end
+
+  def session_zone; connection.select_value('SHOW TIME ZONE'); end
+
+  def set_process_zone(id)
+    java.util.TimeZone.setDefault(java.util.TimeZone.getTimeZone(id))
+  end
+end