pgAudit
Open Source PostgreSQL Audit Logging

Introduction

The PostgreSQL Audit Extension (pgAudit) provides detailed session and/or object audit logging via the standard PostgreSQL logging facility.

The goal of the pgAudit is to provide PostgreSQL users with capability to produce audit logs often required to comply with government, financial, or ISO certifications.

An audit is an official inspection of an individual's or organization's accounts, typically by an independent body. The information gathered by pgAudit is properly called an audit trail or audit log. The term audit log is used in this documentation.

Why pgAudit?

Basic statement logging can be provided by the standard logging facility with log_statement = all. This is acceptable for monitoring and other usages but does not provide the level of detail generally required for an audit. It is not enough to have a list of all the operations performed against the database. It must also be possible to find particular statements that are of interest to an auditor. The standard logging facility shows what the user requested, while pgAudit focuses on the details of what happened while the database was satisfying the request.

For example, an auditor may want to verify that a particular table was created inside a documented maintenance window. This might seem like a simple job for grep, but what if you are presented with something like this (intentionally obfuscated) example:

DO $$
BEGIN
    EXECUTE 'CREATE TABLE import' || 'ant_table (id INT)';
END $$;

Standard logging will give you this:

LOG:  statement: DO $$
BEGIN
    EXECUTE 'CREATE TABLE import' || 'ant_table (id INT)';
END $$;

It appears that finding the table of interest may require some knowledge of the code in cases where tables are created dynamically. This is not ideal since it would be preferable to just search on the table name. This is where pgAudit comes in. For the same input, it will produce this output in the log:

AUDIT: SESSION,33,1,FUNCTION,DO,,,"DO $$
BEGIN
    EXECUTE 'CREATE TABLE import' || 'ant_table (id INT)';
END $$;"
AUDIT: SESSION,33,2,DDL,CREATE TABLE,TABLE,public.important_table,CREATE TABLE important_table (id INT)

Not only is the DO block logged, but substatement 2 contains the full text of the CREATE TABLE with the statement type, object type, and full-qualified name to make searches easy.

When logging SELECT and DML statements, pgAudit can be configured to log a separate entry for each relation referenced in a statement. No parsing is required to find all statements that touch a particular table. In fact, the goal is that the statement text is provided primarily for deep forensics and should not be required for an audit.

Usage Considerations

Depending on settings, it is possible for pgAudit to generate an enormous volume of logging. Be careful to determine exactly what needs to be audit logged in your environment to avoid logging too much.

For example, when working in an OLAP environment it would probably not be wise to audit log inserts into a large fact table. The size of the log file will likely be many times the actual data size of the inserts because the log file is expressed as text. Since logs are generally stored with the OS this may lead to disk space being exhausted very quickly. In cases where it is not possible to limit audit logging to certain tables, be sure to assess the performance impact while testing and allocate plenty of space on the log volume. This may also be true for OLTP environments. Even if the insert volume is not as high, the performance impact of audit logging may still noticeably affect latency.

To limit the number of relations audit logged for SELECT and DML statements, consider using object audit logging (see Object Auditing). Object audit logging allows selection of the relations to be logged allowing for reduction of the overall log volume. However, when new relations are added they must be explicitly added to object audit logging. A programmatic solution where specified tables are excluded from logging and all others are included may be a good option in this case.

PostgreSQL Version Compatibility

pgAudit was developed to support PostgreSQL 9.5 or greater.

In order to support new functionality introduced in each PostgreSQL release, pgAudit maintains a separate branch for each PostgreSQL major version (currently PostgreSQL 9.5 - 11) which will be maintained in a manner similar to the PostgreSQL project.

Aside from bug fixes, no further development is planned for stable branches. New development, if any, will be strictly for next unreleased major version of PostgreSQL.

pgAudit versions relate to PostgreSQL major versions as follows:

• pgAudit v1.4.X is intended to support PostgreSQL 12.

• pgAudit v1.3.X is intended to support PostgreSQL 11.

• pgAudit v1.2.X is intended to support PostgreSQL 10.

• pgAudit v1.1.X is intended to support PostgreSQL 9.6.

• pgAudit v1.0.X is intended to support PostgreSQL 9.5.

Compile and Install

pgAudit can be compiled against an installed copy of PostgreSQL with development packages using PGXS.

Clone the pgAudit extension:

git clone https://github.com/pgaudit/pgaudit.git

Change to pgAudit directory:

cd pgaudit

Checkout REL_11_STABLE branch (note that the stable branch may not exist for unreleased versions of PostgreSQL):

git checkout REL_11_STABLE

Build pgAudit and run regression tests:

make check USE_PGXS=1

Install pgAudit:

make install USE_PGXS=1

Detailed instructions can be found in test/Vagrantfile.

Settings

Settings may be modified only by a superuser. Allowing normal users to change their settings would defeat the point of an audit log.

Settings can be specified globally (in postgresql.conf or using ALTER SYSTEM ... SET), at the database level (using ALTER DATABASE ... SET), or at the role level (using ALTER ROLE ... SET). Note that settings are not inherited through normal role inheritance and SET ROLE will not alter a user's pgAudit settings. This is a limitation of the roles system and not inherent to pgAudit.

The pgAudit extension must be loaded in shared_preload_libraries. Otherwise, an error will be raised at load time and no audit logging will occur. In addition, CREATE EXTENSION pgaudit must be called before pgaudit.log is set. If the pgaudit extension is dropped and needs to be recreated then pgaudit.log must be unset first otherwise an error will be raised.

pgaudit.log

Specifies which classes of statements will be logged by session audit logging. Possible values are:

• READ: SELECT and COPY when the source is a relation or a query.

• WRITE: INSERT, UPDATE, DELETE, TRUNCATE, and COPY when the destination is a relation.

• FUNCTION: Function calls and DO blocks.

• ROLE: Statements related to roles and privileges: GRANT, REVOKE, CREATE/ALTER/DROP ROLE.

• DDL: All DDL that is not included in the ROLE class.

• MISC: Miscellaneous commands, e.g. DISCARD, FETCH, CHECKPOINT, VACUUM, SET.

• MISC_SET: Miscellaneous SET commands, e.g. SET ROLE.

• ALL: Include all of the above.

Multiple classes can be provided using a comma-separated list and classes can be subtracted by prefacing the class with a - sign (see Session Audit Logging).

The default is none.

pgaudit.log_catalog

Specifies that session logging should be enabled in the case where all relations in a statement are in pg_catalog. Disabling this setting will reduce noise in the log from tools like psql and PgAdmin that query the catalog heavily.

The default is on.

pgaudit.log_client

Specifies whether log messages will be visible to a client process such as psql. This setting should generally be left disabled but may be useful for debugging or other purposes.

Note that pgaudit.log_level is only enabled when pgaudit.log_client is on.

The default is off.

pgaudit.log_level

Specifies the log level that will be used for log entries (see Message Severity Levels for valid levels) but note that ERROR, FATAL, and PANIC are not allowed). This setting is used for regression testing and may also be useful to end users for testing or other purposes.

Note that pgaudit.log_level is only enabled when pgaudit.log_client is on; otherwise the default will be used.

The default is log.

pgaudit.log_parameter

Specifies that audit logging should include the parameters that were passed with the statement. When parameters are present they will be included in CSV format after the statement text.

The default is off.

pgaudit.log_relation

Specifies whether session audit logging should create a separate log entry for each relation (TABLE, VIEW, etc.) referenced in a SELECT or DML statement. This is a useful shortcut for exhaustive logging without using object audit logging.

The default is off.

pgaudit.log_statement_once

Specifies whether logging will include the statement text and parameters with the first log entry for a statement/substatement combination or with every entry. Disabling this setting will result in less verbose logging but may make it more difficult to determine the statement that generated a log entry, though the statement/substatement pair along with the process id should suffice to identify the statement text logged with a previous entry.

The default is off.

pgaudit.role

Specifies the master role to use for object audit logging. Multiple audit roles can be defined by granting them to the master role. This allows multiple groups to be in charge of different aspects of audit logging.

There is no default.

Session Audit Logging

Session audit logging provides detailed logs of all statements executed by a user in the backend.

Configuration

Session logging is enabled with the pgaudit.log setting.

Enable session logging for all DML and DDL and log all relations in DML statements:

set pgaudit.log = 'write, ddl';
set pgaudit.log_relation = on;

Enable session logging for all commands except MISC and raise audit log messages as NOTICE:

set pgaudit.log = 'all, -misc';
set pgaudit.log_level = notice;

Example

In this example session audit logging is used for logging DDL and SELECT statements. Note that the insert statement is not logged since the WRITE class is not enabled

SQL:

set pgaudit.log = 'read, ddl';

create table account
(
    id int,
    name text,
    password text,
    description text
);

insert into account (id, name, password, description)
             values (1, 'user1', 'HASH1', 'blah, blah');

select *
    from account;

Log Output:

AUDIT: SESSION,1,1,DDL,CREATE TABLE,TABLE,public.account,create table account
(
    id int,
    name text,
    password text,
    description text
);,<not logged>
AUDIT: SESSION,2,1,READ,SELECT,,,select *
    from account,,<not logged>

Object Audit Logging

Object audit logging logs statements that affect a particular relation. Only SELECT, INSERT, UPDATE and DELETE commands are supported. TRUNCATE is not included in object audit logging.

Object audit logging is intended to be a finer-grained replacement for pgaudit.log = 'read, write'. As such, it may not make sense to use them in conjunction but one possible scenario would be to use session logging to capture each statement and then supplement that with object logging to get more detail about specific relations.

Configuration

Object-level audit logging is implemented via the roles system. The pgaudit.role setting defines the role that will be used for audit logging. A relation (TABLE, VIEW, etc.) will be audit logged when the audit role has permissions for the command executed or inherits the permissions from another role. This allows you to effectively have multiple audit roles even though there is a single master role in any context.

Set pgaudit.role to auditor and grant SELECT and DELETE privileges on the account table. Any SELECT or DELETE statements on the account table will now be logged:

set pgaudit.role = 'auditor';

grant select, delete
   on public.account
   to auditor;

Example

In this example object audit logging is used to illustrate how a granular approach may be taken towards logging of SELECT and DML statements. Note that logging on the account table is controlled by column-level permissions, while logging on the account_role_map table is table-level.

SQL:

set pgaudit.role = 'auditor';

create table account
(
    id int,
    name text,
    password text,
    description text
);

grant select (password)
   on public.account
   to auditor;

select id, name
  from account;

select password
  from account;

grant update (name, password)
   on public.account
   to auditor;

update account
   set description = 'yada, yada';

update account
   set password = 'HASH2';

create table account_role_map
(
    account_id int,
    role_id int
);

grant select
   on public.account_role_map
   to auditor;

select account.password,
       account_role_map.role_id
  from account
       inner join account_role_map
            on account.id = account_role_map.account_id

Log Output:

AUDIT: OBJECT,1,1,READ,SELECT,TABLE,public.account,select password
  from account,<not logged>
AUDIT: OBJECT,2,1,WRITE,UPDATE,TABLE,public.account,update account
   set password = 'HASH2',<not logged>
AUDIT: OBJECT,3,1,READ,SELECT,TABLE,public.account,select account.password,
       account_role_map.role_id
  from account
       inner join account_role_map
            on account.id = account_role_map.account_id,<not logged>
AUDIT: OBJECT,3,1,READ,SELECT,TABLE,public.account_role_map,select account.password,
       account_role_map.role_id
  from account
       inner join account_role_map
            on account.id = account_role_map.account_id,<not logged>

Format

Audit entries are written to the standard logging facility and contain the following columns in comma-separated format. Output is compliant CSV format only if the log line prefix portion of each log entry is removed.

• AUDIT_TYPE - SESSION or OBJECT.

• STATEMENT_ID - Unique statement ID for this session. Each statement ID represents a backend call. Statement IDs are sequential even if some statements are not logged. There may be multiple entries for a statement ID when more than one relation is logged.

• SUBSTATEMENT_ID - Sequential ID for each sub-statement within the main statement. For example, calling a function from a query. Sub-statement IDs are continuous even if some sub-statements are not logged. There may be multiple entries for a sub-statement ID when more than one relation is logged.

• CLASS - e.g. READ, ROLE (see pgaudit.log).

• COMMAND - e.g. ALTER TABLE, SELECT.

• OBJECT_TYPE - TABLE, INDEX, VIEW, etc. Available for SELECT, DML and most DDL statements.

• OBJECT_NAME - The fully-qualified object name (e.g. public.account). Available for SELECT, DML and most DDL statements.

• STATEMENT - Statement executed on the backend.

• PARAMETER - If pgaudit.log_parameter is set then this field will contain the statement parameters as quoted CSV or <none> if there are no parameters. Otherwise, the field is <not logged>.

Use log_line_prefix to add any other fields that are needed to satisfy your audit log requirements. A typical log line prefix might be '%m %u %d [%p]: ' which would provide the date/time, user name, database name, and process id for each audit log.

Caveats

Object renames are logged under the name they were renamed to. For example, renaming a table will produce the following result:

ALTER TABLE test RENAME TO test2;

AUDIT: SESSION,36,1,DDL,ALTER TABLE,TABLE,public.test2,ALTER TABLE test RENAME TO test2,<not logged>

It is possible to have a command logged more than once. For example, when a table is created with a primary key specified at creation time the index for the primary key will be logged independently and another audit log will be made for the index under the create entry. The multiple entries will however be contained within one statement ID.

Autovacuum and Autoanalyze are not logged.

Statements that are executed after a transaction enters an aborted state will not be audit logged. However, the statement that caused the error and any subsequent statements executed in the aborted transaction will be logged as ERRORs by the standard logging facility.

Authors

The PostgreSQL Audit Extension is based on the 2ndQuadrant pgaudit project authored by Simon Riggs, Abhijit Menon-Sen, and Ian Barwick and submitted as an extension to PostgreSQL core. Additional development has been done by David Steele of Crunchy Data.