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Compatibility with Earlier Versions

Updated at: Jul 15, 2020 GMT+08:00

This section describes the parameter control of the downward compatibility and external compatibility features of DWS. Backward compatibility of the database system provides support for the application of databases of earlier versions. This section describes parameters used for controlling backward compatibility of a database.

array_nulls

Parameter description: Determines whether the array input parser recognizes unquoted NULL as a null array element.

Type: USERSET

Value range: Boolean

  • on indicates that null values can be entered in arrays.
  • off indicates backward compatibility with the old behavior. Arrays containing NULL values can still be created when this parameter is set to off.

Default value: on

backslash_quote

Parameter description: Determines whether a single quotation mark can be represented by \' in a string text.

Type: USERSET

When the string text meets the SQL standards, \ has no other meanings. This parameter only affects the handling of non-standard-conforming string texts, including escape string syntax (E'...').

Value range: enumerated values

  • on indicates that the use of \' is always allowed.
  • off indicates that the use of \' is rejected.
  • safe_encoding indicates that the use of \' is allowed only when client encoding does not allow ASCII \ within a multibyte character.

Default value: safe_encoding

default_with_oids

Parameter description: Determines whether CREATE TABLE and CREATE TABLE AS include an OID field in newly-created tables if neither WITH OIDS nor WITHOUT OIDS is specified. It also determines whether OIDs will be included in tables created by SELECT INTO.

It is not recommended that OIDs be used in user tables. Therefore, this parameter is set to off by default. When OIDs are required for a particular table, WITH OIDS needs to be specified during the table creation.

Type: USERSET

Value range: Boolean

  • on indicates CREATE TABLE and CREATE TABLE AS can include an OID field in newly-created tables.
  • off indicates CREATE TABLE and CREATE TABLE AS cannot include any OID field in newly-created tables.

Default value: off

escape_string_warning

Parameter description: Specifies a warning on directly using a backslash (\) as an escape in an ordinary character string.

  • Applications that wish to use a backslash (\) as an escape need to be modified to use escape string syntax (E'...'). This is because the default behavior of ordinary character strings is now to treat the backslash as an ordinary character in each SQL standard.
  • This variable can be enabled to help locate codes that need to be changed.

Type: USERSET

Value range: Boolean

Default value: on

lo_compat_privileges

Parameter description: Determines whether to enable backward compatibility for the privilege check of large objects.

Type: SUSET

Value range: Boolean

on indicates that the privilege check is disabled when users read or modify large objects. This setting is compatible with versions earlier than PostgreSQL 9.0.

Default value: off

quote_all_identifiers

Parameter description: When the database generates SQL, this parameter forcibly quotes all identifiers even if they are not keywords. This will affect the output of EXPLAIN as well as the results of functions, such as pg_get_viewdef. For details, see the --quote-all-identifiers parameter of gs_dump.

Type: USERSET

Value range: Boolean

  • on indicates the forcible quotation function is enabled.
  • off indicates the forcible quotation function is disabled.

Default value: off

sql_inheritance

Parameter description: Determines whether to inherit semantics.

Type: USERSET

Value range: Boolean

off indicates that child tables cannot be accessed by various commands. That is, an ONLY keyword is used by default. This setting is compatible with versions earlier than PostgreSQL 7.1.

Default value: on

standard_conforming_strings

Parameter description: Determines whether ordinary string texts ('...') treat backslashes as ordinary texts as specified in the SQL standard.

  • Applications can check this parameter to determine how string texts will be processed.
  • It is recommended that characters be escaped by using the escape string syntax (E'...').

Type: USERSET

Value range: Boolean

  • on indicates that the function is enabled.
  • off indicates that the function is disabled.

Default value: on

synchronize_seqscans

Parameter description: Controls sequential scans of tables to synchronize with each other. Concurrent scans read the same data block about at the same time and share the I/O workload.

Type: USERSET

Value range: Boolean

  • on indicates that a scan may start in the middle of the table and then "wrap around" the end to cover all rows to synchronize with the activity of scans already in progress. This may result in unpredictable changes in the row ordering returned by queries that have no ORDER BY clause.
  • off indicates that the scan always starts from the table heading.

Default value: on

enable_beta_features

Parameter description: Controls whether certain limited features, such as GDS table join, are available. These features are not explicitly prohibited in earlier versions, but are not recommended due to their limitations in certain scenarios.

Type: USERSET

Value range: Boolean

  • on indicates that the features are enabled and forward compatible, but may incur errors in certain scenarios.
  • off indicates that the features are disabled.

Default value: off

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