Compatibility with Earlier Versions

This section describes the parameter control of the downward compatibility and external compatibility features of the MogDB database. A backward compatible database supports applications of earlier versions. This section describes parameters used for controlling backward compatibility of a database.

array_nulls

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

This parameter is a USERSET parameter. Set it based on instructions provided in Table 2 Methods for setting GUC parameters.

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: controls whether a single quotation mark can be represented by ' in a string text.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 2 Methods for setting GUC parameters.

NOTICE: 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

escape_string_warning

Parameter description: specifies a warning on directly using a backslash () as an escape in an ordinary 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 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.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 2 Methods for setting GUC parameters.

Value range: Boolean

Default value: on

lo_compat_privileges

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

This parameter is a SUSET parameter. Set it based on instructions provided in Table 2 Methods for setting GUC parameters.

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.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 2 Methods for setting GUC parameters.

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: Specifies whether to inherit semantics. This parameter specifies the access policy of descendant tables. off indicates that subtables cannot be accessed by commands. That is, the ONLY keyword is used by default. This setting is compatible with earlier versions.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 2 Methods for setting GUC parameters.

Value range: Boolean

• on indicates that the subtable can be accessed.
• off indicates that the subtable cannot be accessed.

Default value: on

standard_conforming_strings

Parameter description: Specifies 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'…').

This parameter is a USERSET parameter. Set it based on instructions provided in Table 2 Methods for setting GUC parameters.

Value range: Boolean

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

Default value: on

synchronize_seqscans

Parameter description: Specifies 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.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 2 Methods for setting GUC parameters.

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_poc_features

Parameter description: Specifies whether to enable some features that are not officially released and are used only for POC verification. Exercise caution when enabling these extended features because they may cause errors in some scenarios. This parameter will not normally take effect in every LTS version, e.g. 2.0; this parameter will normally take effect in every preview version, e.g. 2.1. MogDB 2.1 Row-store Table Compression and SubPartition are affected by this parameter, see MogDB 2.1.0 New Features for more information.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 2 Methods for setting GUC parameters.

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