The gp_toolkit Administrative Schema

Greenplum Database provides an administrative schema called gp_toolkit that you can use to query the system catalogs, log files, and operating environment for system status information. The gp_toolkit schema contains a number of views that you can access using SQL commands. The gp_toolkit schema is accessible to all database users, although some objects may require superuser permissions. For convenience, you may want to add the gp_toolkit schema to your schema search path. For example:

=> ALTER ROLE myrole SET search_path TO myschema,gp_toolkit;

This documentation describes the most useful views in gp_toolkit. You may notice other objects (views, functions, and external tables) within the gp_toolkit schema that are not described in this documentation (these are supporting objects to the views described in this section).

Warning: Do not change database objects in the gp_toolkit schema. Do not create database objects in the schema. Changes to objects in the schema might affect the accuracy of administrative information returned by schema objects. Any changes made in the gp_toolkit schema are lost when the database is backed up and then restored with the gpbackup and gprestore utilities.

These are the categories for views in the gp_toolkit schema.

• Checking for Tables that Need Routine Maintenance

• Checking for Locks

• Checking Append-Optimized Tables

• Viewing Greenplum Database Server Log Files

• Checking Server Configuration Files

• Checking for Failed Segments

• Checking Resource Group Activity and Status

• Checking Resource Queue Activity and Status

• Checking Query Disk Spill Space Usage

• Viewing Users and Groups (Roles)

• Checking Database Object Sizes and Disk Space

• Checking for Uneven Data Distribution

Parent topic: Greenplum Database Reference Guide

Checking for Tables that Need Routine Maintenance

The following views can help identify tables that need routine table maintenance (VACUUM and/or ANALYZE).

• gp_bloat_diag
• gp_stats_missing

The VACUUM or VACUUM FULL command reclaims disk space occupied by deleted or obsolete rows. Because of the MVCC transaction concurrency model used in Greenplum Database, data rows that are deleted or updated still occupy physical space on disk even though they are not visible to any new transactions. Expired rows increase table size on disk and eventually slow down scans of the table.

The ANALYZE command collects column-level statistics needed by the query optimizer. Greenplum Database uses a cost-based query optimizer that relies on database statistics. Accurate statistics allow the query optimizer to better estimate selectivity and the number of rows retrieved by a query operation in order to choose the most efficient query plan.

Parent topic: The gp_toolkit Administrative Schema

gp_bloat_diag

This view shows regular heap-storage tables that have bloat (the actual number of pages on disk exceeds the expected number of pages given the table statistics). Tables that are bloated require a VACUUM or a VACUUM FULL in order to reclaim disk space occupied by deleted or obsolete rows. This view is accessible to all users, however non-superusers will only be able to see the tables that they have permission to access.

Note: For diagnostic functions that return append-optimized table information, see Checking Append-Optimized Tables.

gp_stats_missing

This view shows tables that do not have statistics and therefore may require an ANALYZE be run on the table.

Checking for Locks

When a transaction accesses a relation (such as a table), it acquires a lock. Depending on the type of lock acquired, subsequent transactions may have to wait before they can access the same relation. For more information on the types of locks, see “Managing Data” in the Greenplum Database Administrator Guide. Greenplum Database resource queues (used for resource management) also use locks to control the admission of queries into the system.

The gp_locks_* family of views can help diagnose queries and sessions that are waiting to access an object due to a lock.

• gp_locks_on_relation
• gp_locks_on_resqueue

Parent topic: The gp_toolkit Administrative Schema

gp_locks_on_relation

This view shows any locks currently being held on a relation, and the associated session information about the query associated with the lock. For more information on the types of locks, see “Managing Data” in the Greenplum Database Administrator Guide. This view is accessible to all users, however non-superusers will only be able to see the locks for relations that they have permission to access.

gp_locks_on_resqueue

Note: The gp_locks_on_resqueue view is valid only when resource queue-based resource management is active.

This view shows any locks currently being held on a resource queue, and the associated session information about the query associated with the lock. This view is accessible to all users, however non-superusers will only be able to see the locks associated with their own sessions.

Checking Append-Optimized Tables

The gp_toolkit schema includes a set of diagnostic functions you can use to investigate the state of append-optimized tables.

When an append-optimized table (or column-oriented append-optimized table) is created, another table is implicitly created, containing metadata about the current state of the table. The metadata includes information such as the number of records in each of the table’s segments.

Append-optimized tables may have non-visible rows—rows that have been updated or deleted, but remain in storage until the table is compacted using VACUUM. The hidden rows are tracked using an auxiliary visibility map table, or visimap.

The following functions let you access the metadata for append-optimized and column-oriented tables and view non-visible rows. Some of the functions have two versions: one that takes the oid of the table, and one that takes the name of the table. The latter version has “_name” appended to the function name.

Parent topic: The gp_toolkit Administrative Schema

__gp_aovisimap_compaction_info(oid)

This function displays compaction information for an append-optimized table. The information is for the on-disk data files on Greenplum Database segments that store the table data. You can use the information to determine the data files that will be compacted by a VACUUM operation on an append-optimized table.

Note: Until a VACUUM operation deletes the row from the data file, deleted or updated data rows occupy physical space on disk even though they are hidden to new transactions. The configuration parameter gp_appendonly_compaction controls the functionality of the VACUUM command.

This table describes the __gp_aovisimap_compaction_info function output table.

__gp_aoseg_name(‘table_name’)

This function returns metadata information contained in the append-optimized table’s on-disk segment file.

__gp_aoseg_history(oid)

This function returns metadata information contained in the append-optimized table’s on-disk segment file. It displays all different versions (heap tuples) of the aoseg meta information. The data is complex, but users with a deep understanding of the system may find it usefulfor debugging.

The input argument is the oid of the append-optimized table.

Call __gp_aoseg_history_name(‘table_name’) to get the same result with the table name as an argument.

__gp_aocsseg(oid)

This function returns metadata information contained in a column-oriented append-optimized table’s on-disk segment file, excluding non-visible rows. Each row describes a segment for a column in the table.

The input argument is the oid of a column-oriented append-optimized table. Call as __gp_aocsseg_name(‘table_name’) to get the same result with the table name as an argument.

__gp_aocsseg_history(oid)

This function returns metadata information contained in a column-oriented append-optimized table’s on-disk segment file. Each row describes a segment for a column in the table. The data is complex, but users with a deep understanding of the system may find it useful for debugging.

The input argument is the oid of a column-oriented append-optimized table. Call as __gp_aocsseg_history_name(‘table_name’) to get the same result with the table name as argument.

__gp_aovisimap(oid)

This function returns the tuple id, the segment file, and the row number of each non-visible tuple according to the visibility map.

The input argument is the oid of an append-optimized table.

Use __gp_aovisimap_name(‘table_name’) to get the same result with the table name as argument.

__gp_aovisimap_hidden_info(oid)

This function returns the numbers of hidden and visible tuples in the segment files for an append-optimized table.

The input argument is the oid of the append-optimized table.

Call __gp_aovisimap_hidden_info_name(‘table_name’) to get the same result with a table name argument.

__gp_aovisimap_entry(oid)

This function returns information about each visibility map entry for the table.

The input argument is the oid of an append-optimized table.

Call __gp_aovisimap_entry_name(‘table_name’) to get the same result with a table name argument.

Viewing Greenplum Database Server Log Files

Each component of a Greenplum Database system (master, standby master, primary segments, and mirror segments) keeps its own server log files. The gp_log_* family of views allows you to issue SQL queries against the server log files to find particular entries of interest. The use of these views require superuser permissions.

• gp_log_command_timings
• gp_log_database
• gp_log_master_concise
• gp_log_system

Parent topic: The gp_toolkit Administrative Schema

gp_log_command_timings

This view uses an external table to read the log files on the master and report the execution time of SQL commands executed in a database session. The use of this view requires superuser permissions.

gp_log_database

This view uses an external table to read the server log files of the entire Greenplum system (master, segments, and mirrors) and lists log entries associated with the current database. Associated log entries can be identified by the session id (logsession) and command id (logcmdcount). The use of this view requires superuser permissions.

gp_log_master_concise

This view uses an external table to read a subset of the log fields from the master log file. The use of this view requires superuser permissions.

gp_log_system

This view uses an external table to read the server log files of the entire Greenplum system (master, segments, and mirrors) and lists all log entries. Associated log entries can be identified by the session id (logsession) and command id (logcmdcount). The use of this view requires superuser permissions.

Checking Server Configuration Files

Each component of a Greenplum Database system (master, standby master, primary segments, and mirror segments) has its own server configuration file (postgresql.conf). The following gp_toolkit objects can be used to check parameter settings across all primary postgresql.conf files in the system:

• gp_param_setting(‘parameter_name’)
• gp_param_settings_seg_value_diffs

Parent topic: The gp_toolkit Administrative Schema

gp_param_setting(‘parameter_name’)

This function takes the name of a server configuration parameter and returns the postgresql.conf value for the master and each active segment. This function is accessible to all users.

Example:

SELECT * FROM gp_param_setting('max_connections');

gp_param_settings_seg_value_diffs

Server configuration parameters that are classified as local parameters (meaning each segment gets the parameter value from its own postgresql.conf file), should be set identically on all segments. This view shows local parameter settings that are inconsistent. Parameters that are supposed to have different values (such as port) are not included. This view is accessible to all users.

Checking for Failed Segments

The gp_pgdatabase_invalid view can be used to check for down segments.

Parent topic: The gp_toolkit Administrative Schema

gp_pgdatabase_invalid

This view shows information about segments that are marked as down in the system catalog. This view is accessible to all users.

Checking Resource Group Activity and Status

Note: The resource group activity and status views described in this section are valid only when resource group-based resource management is active.

Resource groups manage transactions to avoid exhausting system CPU and memory resources. Every database user is assigned a resource group. Greenplum Database evaluates every transaction submitted by a user against the limits configured for the user’s resource group before running the transaction.

You can use the gp_resgroup_config view to check the configuration of each resource group. You can use the gp_resgroup_status view to display the current transaction status and resource usage of each resource group.

• gp_resgroup_config
• gp_resgroup_status

Parent topic: The gp_toolkit Administrative Schema

gp_resgroup_config

The gp_resgroup_config view allows administrators to see the current CPU, memory, and concurrency limits for a resource group. The view also displays proposed limit settings. A proposed limit will differ from the current limit when the limit has been altered, but the new value could not be immediately applied.

This view is accessible to all users.

gp_resgroup_status

The gp_resgroup_status view allows administrators to see status and activity for a resource group. It shows how many queries are waiting to run and how many queries are currently active in the system for each resource group. The view also displays current memory and CPU usage for the resource group.

Note: Resource groups use the Linux control groups (cgroups) configured on the host systems. The cgroups are used to manage host system resources. When resource groups use cgroups that are as part of a nested set of cgroups, resource group limits are relative to the parent cgroup allotment. For information about nested cgroups and Greenplum Database resource group limits, see Understanding Role and Component Resource Groups.

This view is accessible to all users.

The cpu_usage field is a JSON-formatted, key:value string that identifies, for each resource group, the per-segment CPU usage percentage. The key is segment id, the value is the percentage of CPU usage by the resource group on the segment host. The total CPU usage of all segments running on a segment host should not exceed the gp_resource_group_cpu_limit. Example cpu_usage column output:

{"-1":0.01, "0":0.31, "1":0.31}

In this example, segment 0 and segment 1 are running on the same host; their CPU usage is the same.

The memory_usage field is also a JSON-formatted, key:value string. The string contents differ depending upon the type of resource group. For each resource group that you assign to a role (default memory auditor vmtracker), this string identifies the used, available, granted, and proposed fixed and shared memory quota allocations on each segment. The key is segment id. The values are memory values displayed in MB units. The following example shows memory_usage column output for a single segment for a resource group that you assign to a role:

"0":{"used":0, "available":76, "quota_used":-1, "quota_available":60, "quota_granted":60, "quota_proposed":60, "shared_used":0, "shared_available":16, "shared_granted":16, "shared_proposed":16}

For each resource group that you assign to an external component, the memory_usage JSON-formatted string identifies the memory used and the memory limit on each segment. The following example shows memory_usage column output for an external component resource group for a single segment:

"1":{"used":11, "limit_granted":15}

Checking Resource Queue Activity and Status

Note: The resource queue activity and status views described in this section are valid only when resource queue-based resource management is active.

The purpose of resource queues is to limit the number of active queries in the system at any given time in order to avoid exhausting system resources such as memory, CPU, and disk I/O. All database users are assigned to a resource queue, and every statement submitted by a user is first evaluated against the resource queue limits before it can run. The gp_resq_* family of views can be used to check the status of statements currently submitted to the system through their respective resource queue. Note that statements issued by superusers are exempt from resource queuing.

• gp_resq_activity
• gp_resq_activity_by_queue
• gp_resq_priority_statement
• gp_resq_role
• gp_resqueue_status

Parent topic: The gp_toolkit Administrative Schema

gp_resq_activity

For the resource queues that have active workload, this view shows one row for each active statement submitted through a resource queue. This view is accessible to all users.

gp_resq_activity_by_queue

For the resource queues that have active workload, this view shows a summary of queue activity. This view is accessible to all users.

gp_resq_priority_statement

This view shows the resource queue priority, session ID, and other information for all statements currently running in the Greenplum Database system. This view is accessible to all users.

gp_resq_role

This view shows the resource queues associated with a role. This view is accessible to all users.

gp_resqueue_status

This view allows administrators to see status and activity for a resource queue. It shows how many queries are waiting to run and how many queries are currently active in the system from a particular resource queue.

Checking Query Disk Spill Space Usage

The gp_workfile_* views show information about all the queries that are currently using disk spill space. Greenplum Database creates work files on disk if it does not have sufficient memory to execute the query in memory. This information can be used for troubleshooting and tuning queries. The information in the views can also be used to specify the values for the Greenplum Database configuration parameters gp_workfile_limit_per_query and gp_workfile_limit_per_segment.

• gp_workfile_entries
• gp_workfile_usage_per_query
• gp_workfile_usage_per_segment

Parent topic: The gp_toolkit Administrative Schema

gp_workfile_entries

This view contains one row for each operator using disk space for workfiles on a segment at the current time. The view is accessible to all users, however non-superusers only to see information for the databases that they have permission to access.

gp_workfile_usage_per_query

This view contains one row for each query using disk space for workfiles on a segment at the current time. The view is accessible to all users, however non-superusers only to see information for the databases that they have permission to access.

gp_workfile_usage_per_segment

This view contains one row for each segment. Each row displays the total amount of disk space used for workfiles on the segment at the current time. The view is accessible to all users, however non-superusers only to see information for the databases that they have permission to access.

Viewing Users and Groups (Roles)

It is frequently convenient to group users (roles) together to ease management of object privileges: that way, privileges can be granted to, or revoked from, a group as a whole. In Greenplum Database this is done by creating a role that represents the group, and then granting membership in the group role to individual user roles.

The gp_roles_assigned view can be used to see all of the roles in the system, and their assigned members (if the role is also a group role).

Parent topic: The gp_toolkit Administrative Schema

gp_roles_assigned

This view shows all of the roles in the system, and their assigned members (if the role is also a group role). This view is accessible to all users.

Checking Database Object Sizes and Disk Space

The gp_size_* family of views can be used to determine the disk space usage for a distributed Greenplum Database, schema, table, or index. The following views calculate the total size of an object across all primary segments (mirrors are not included in the size calculations).

• gp_size_of_all_table_indexes
• gp_size_of_database
• gp_size_of_index
• gp_size_of_partition_and_indexes_disk
• gp_size_of_schema_disk
• gp_size_of_table_and_indexes_disk
• gp_size_of_table_and_indexes_licensing
• gp_size_of_table_disk
• gp_size_of_table_uncompressed
• gp_disk_free

The table and index sizing views list the relation by object ID (not by name). To check the size of a table or index by name, you must look up the relation name (relname) in the pg_class table. For example:

SELECT relname as name, sotdsize as size, sotdtoastsize as 
toast, sotdadditionalsize as other 
FROM gp_size_of_table_disk as sotd, pg_class 
WHERE sotd.sotdoid=pg_class.oid ORDER BY relname;

Parent topic: The gp_toolkit Administrative Schema

gp_size_of_all_table_indexes

This view shows the total size of all indexes for a table. This view is accessible to all users, however non-superusers will only be able to see relations that they have permission to access.

gp_size_of_database

This view shows the total size of a database. This view is accessible to all users, however non-superusers will only be able to see databases that they have permission to access.

gp_size_of_index

This view shows the total size of an index. This view is accessible to all users, however non-superusers will only be able to see relations that they have permission to access.

gp_size_of_partition_and_indexes_disk

This view shows the size on disk of partitioned child tables and their indexes. This view is accessible to all users, however non-superusers will only be able to see relations that they have permission to access..

gp_size_of_schema_disk

This view shows schema sizes for the public schema and the user-created schemas in the current database. This view is accessible to all users, however non-superusers will be able to see only the schemas that they have permission to access.

gp_size_of_table_and_indexes_disk

This view shows the size on disk of tables and their indexes. This view is accessible to all users, however non-superusers will only be able to see relations that they have permission to access.

gp_size_of_table_and_indexes_licensing

This view shows the total size of tables and their indexes for licensing purposes. The use of this view requires superuser permissions.

gp_size_of_table_disk

This view shows the size of a table on disk. This view is accessible to all users, however non-superusers will only be able to see tables that they have permission to access

gp_size_of_table_uncompressed

This view shows the uncompressed table size for append-optimized (AO) tables. Otherwise, the table size on disk is shown. The use of this view requires superuser permissions.

gp_disk_free

This external table runs the df (disk free) command on the active segment hosts and reports back the results. Inactive mirrors are not included in the calculation. The use of this external table requires superuser permissions.

Checking for Uneven Data Distribution

All tables in Greenplum Database are distributed, meaning their data is divided across all of the segments in the system. If the data is not distributed evenly, then query processing performance may decrease. The following views can help diagnose if a table has uneven data distribution:

• gp_skew_coefficients
• gp_skew_idle_fractions

Parent topic: The gp_toolkit Administrative Schema

gp_skew_coefficients

This view shows data distribution skew by calculating the coefficient of variation (CV) for the data stored on each segment. This view is accessible to all users, however non-superusers will only be able to see tables that they have permission to access

gp_skew_idle_fractions

This view shows data distribution skew by calculating the percentage of the system that is idle during a table scan, which is an indicator of processing data skew. This view is accessible to all users, however non-superusers will only be able to see tables that they have permission to access