Redact audit log fields¶

Audit events that carry SQL statement text can leak sensitive values into the audit log. Examples include credentials, personal data, and secret literals. The Audit Log Filter can rewrite that text as a statement digest before the event is written. The log records what kind of statement ran without capturing the literal values.

This page covers the print and replace mechanism. For base filter authoring, see Write audit_log_filter definitions.

What can be replaced¶

Only two fields are replaceable, and only with the query_digest function:

Event class	Replaceable field
`general`	`general_query.str`
`table_access`	`query.str`

Replacement happens during filtering, so the choice between literal text and digest applies regardless of which log format (XML or JSON) writes the event.

Shape¶

A print item goes inside a class or event block:

"print": {
  "field": {
    "name": "field_name",
    "print": condition,
    "replace": replacement_value
  }
}

name — the replaceable field from the preceding table.
print — a condition. When the condition evaluates to true, the field is kept. When the condition evaluates to false, the field is replaced. Use "print": false to replace unconditionally.
replace — the replacement value, specified as a function item. Only query_digest (with no arguments) is permitted.

The conditional form lets you mix redacted and literal statements in the same filter.

Example 1: Redact every `general` event¶

Replace statement text in every general event with its digest:

{
  "filter": {
    "class": {
      "name": "general",
      "print": {
        "field": {
          "name": "general_query.str",
          "print": false,
          "replace": {
            "function": { "name": "query_digest" }
          }
        }
      }
    }
  }
}

Example 2: Redact both statement-carrying classes¶

general and table_access both carry statement text. Combine them into one filter:

{
  "filter": {
    "class": [
      {
        "name": "general",
        "print": {
          "field": {
            "name": "general_query.str",
            "print": false,
            "replace": { "function": { "name": "query_digest" } }
          }
        }
      },
      {
        "name": "table_access",
        "print": {
          "field": {
            "name": "query.str",
            "print": false,
            "replace": { "function": { "name": "query_digest" } }
          }
        }
      }
    ]
  }
}

The resulting audit stream contains only digests, with no literal SQL text. The output is a common baseline for PCI and PII environments.

Example 3: Redact only specific events¶

Scope replacement to a subset of events by nesting print inside an event block. The following filter redacts query.str on insert and update table_access events but leaves read and delete alone:

{
  "filter": {
    "class": {
      "name": "table_access",
      "event": {
        "name": ["insert", "update"],
        "print": {
          "field": {
            "name": "query.str",
            "print": false,
            "replace": { "function": { "name": "query_digest" } }
          }
        }
      }
    }
  }
}

Example 4: Redact account-management statements¶

query_digest with an argument is a Boolean comparator. The comparator is useful in a log condition to decide whether to log an event based on the digest. Combined with field checks, you can log and redact only specific statement types. The following filter matches general/status events for account-management DDL and replaces the literal statement with the digest:

{
  "filter": {
    "class": {
      "name": "general",
      "event": {
        "name": "status",
        "print": {
          "field": {
            "name": "general_query.str",
            "print": false,
            "replace": {
              "function": { "name": "query_digest" }
            }
          }
        },
        "log": {
          "or": [
            { "field": { "name": "general_sql_command.str", "value": "alter_user" } },
            { "field": { "name": "general_sql_command.str", "value": "alter_user_default_role" } },
            { "field": { "name": "general_sql_command.str", "value": "create_role" } },
            { "field": { "name": "general_sql_command.str", "value": "create_user" } }
          ]
        }
      }
    }
  }
}

For the full set of general_sql_command.str values, see Test event field values.

Conditional redaction¶

To keep literal text for most statements and redact only specific ones (or the reverse), use query_digest as a comparator inside print. With an argument, the function returns true when the active statement digest equals the argument.

Keep the literal text when the digest matches SELECT ?, and replace otherwise:

"print": {
  "field": {
    "name": "general_query.str",
    "print": {
      "function": {
        "name": "query_digest",
        "args": "SELECT ?"
      }
    },
    "replace": {
      "function": { "name": "query_digest" }
    }
  }
}

Invert with not to redact only the matching statements and keep literal text for the rest:

"print": {
  "field": {
    "name": "general_query.str",
    "print": {
      "not": {
        "function": {
          "name": "query_digest",
          "args": "SELECT ?"
        }
      }
    },
    "replace": {
      "function": { "name": "query_digest" }
    }
  }
}