18.104.22.168 Rewriter Query Rewrite Plugin Reference
The following discussion serves as a reference to these components associated with the
Rewriter query rewrite plugin:
Rewriterrules table in the
Rewriterprocedures and functions
Rewritersystem and status variables
rewrite_rules table in the
query_rewrite database provides persistent storage for the rules that the
Rewriter plugin uses to decide whether to rewrite statements.
Users communicate with the plugin by modifying the set of rules stored in this table. The plugin communicates information to users by setting the table's
The rules table is loaded into the plugin by the
flush_rewrite_rules stored procedure. Unless that procedure has been called following the most recent table modification, the table contents do not necessarily correspond to the set of rules the plugin is using.
rewrite_rules table has these columns:
The rule ID. This column is the table primary key. You can use the ID to uniquely identify any rule.
The template that indicates the pattern for statements that the rule matches. Use
?to represent parameter markers that match data values.
The database used to match unqualified table names in statements. Qualified table names in statements match qualified names in the pattern if corresponding database and table names are identical. Unqualified table names in statements match unqualified names in the pattern only if the default database is the same as
pattern_databaseand the table names are identical.
The template that indicates how to rewrite statements matching the
patterncolumn value. Use
?to represent parameter markers that match data values. In rewritten statements, the plugin replaces
?parameter markers in
replacementusing data values matched by the corresponding markers in
Whether the rule is enabled. Load operations (performed by invoking the
flush_rewrite_rules()stored procedure) load the rule from the table into the
Rewriterin-memory cache only if this column is
This column makes it possible to deactivate a rule without removing it: Set the column to a value other than
YESand reload the table into the plugin.
The plugin uses this column for communicating with users. If no error occurs when the rules table is loaded into memory, the plugin sets the
NULL. A non-
NULLvalue indicates an error and the column contents are the error message. Errors can occur under these circumstances:
Either the pattern or the replacement is an incorrect SQL statement that produces syntax errors.
The replacement contains more
?parameter markers than the pattern.
If a load error occurs, the plugin also sets the
Rewriter_reload_errorstatus variable to
This column is used for debugging and diagnostics. If the column exists when the rules table is loaded into memory, the plugin updates it with the pattern digest. This column may be useful if you are trying to determine why some statement fails to be rewritten.
This column is used for debugging and diagnostics. If the column exists when the rules table is loaded into memory, the plugin updates it with the normalized form of the pattern. This column may be useful if you are trying to determine why some statement fails to be rewritten.
Rewriter plugin operation uses a stored procedure that loads the rules table into its in-memory cache, and a helper user-defined function (UDF). Under normal operation, users invoke only the stored procedure. The UDF is intended to be invoked by the stored procedure, not directly by users.
This stored procedure uses the
load_rewrite_rules()UDF to load the contents of the
rewrite_rulestable into the
Rewriterin-memory cache. After loading the table, it also clears the query cache.
Invoke this procedure after you modify the rules table to cause the plugin to update its cache from the new table contents. If any errors occur, the plugin sets the
messagecolumn for the appropriate rule rows in the table and sets the
Rewriter_reload_errorstatus variable to
This UDF is a helper routine used by the
Rewriter query rewrite plugin supports the following system variables. These variables are available only if the plugin is installed (see Section 22.214.171.124, “Installing or Uninstalling the Rewriter Query Rewrite Plugin”).
Rewriter query rewrite plugin supports the following status variables. These variables are available only if the plugin is installed (see Section 126.96.36.199, “Installing or Uninstalling the Rewriter Query Rewrite Plugin”).
The number of rewrite plugin rewrite rules successfully loaded from the
rewrite_rulestable into memory for use by the
The number of times the
rewrite_rulestable has been loaded into the in-memory cache used by the
The number of queries rewritten by the
Rewriterquery rewrite plugin since it was loaded.
Whether an error occurred the most recent time that the
rewrite_rulestable was loaded into the in-memory cache used by the
Rewriterplugin. If the value is
OFF, no error occurred. If the value is
ON, an error occurred; check the
messagecolumn of the
rewriter_rulestable for error messages.