STATISTICS VIEW · Statistics view

pg_stat_io

PostgreSQL documentation ↗Source definition ↗

The pg_stat_io view will contain one row for each combination of backend type, target I/O object, and I/O context, showing cluster-wide I/O statistics. Combinations which do not make sense are omitted. Currently, I/O on relations (e.g. tables, indexes) and WAL activity are tracked. However, relation I/O which bypasses shared buffers (e.g. when moving a table from one tablespace to another) is currently not tracked. Some backend types never perform I/O operations on some I/O objects and/or in some I/O contexts. These rows are omitted from the view. For example, the checkpointer does not checkpoint temporary tables, so there will be no rows for backend_type checkpointer and object temp relation. In addition, some I/O operations will never be performed either by certain backend types or on certain I/O objects and/or in certain I/O contexts. These cells will be NULL. For example, temporary tables are not fsynced, so fsyncs will be NULL for object temp relation. Also, the background writer does not perform reads, so reads will be NULL in rows for backend_type background writer. For the object wal, fsyncs and fsync_time track the fsync activity of WAL files done in issue_xlog_fsync. writes and write_time track the write activity of WAL files done in XLogWrite. See Section 28.5 for more information. pg_stat_io can be used to inform database tuning. For example:

First seen PG 16Last seen PG 19Columns 20

9.0 9.1 9.2 9.3 9.4 9.5 9.6 10 11 12 13 14 15 16 17 18 19^β3

Checked column by column against a PostgreSQL 18.6 instance · Raw measurement record ↗

Columns PostgreSQL 18

pg_stat_io

COLUMN	TYPE	DESCRIPTION
`backend_type`	`text`	Type of backend (e.g. background worker, autovacuum worker). See pg_stat_activity for more information on backend_types. Some backend_types do not accumulate I/O operation statistics and will not be included in the view.
`object`	`text`	Target object of an I/O operation. Possible values are:
`context`	`text`	The context of an I/O operation. Possible values are:
`reads`	`bigint`	Number of read operations.
`read_bytes`	`numeric`	The total size of read operations in bytes.
`read_time`	`double precision`	Time spent waiting for read operations in milliseconds (if track_io_timing is enabled and object is not wal, or if track_wal_io_timing is enabled and object is wal, otherwise zero)
`writes`	`bigint`	Number of write operations.
`write_bytes`	`numeric`	The total size of write operations in bytes.
`write_time`	`double precision`	Time spent waiting for write operations in milliseconds (if track_io_timing is enabled and object is not wal, or if track_wal_io_timing is enabled and object is wal, otherwise zero)
`writebacks`	`bigint`	Number of units of size BLCKSZ (typically 8kB) which the process requested the kernel write out to permanent storage.
`writeback_time`	`double precision`	Time spent waiting for writeback operations in milliseconds (if track_io_timing is enabled, otherwise zero). This includes the time spent queueing write-out requests and, potentially, the time spent to write out the dirty data.
`extends`	`bigint`	Number of relation extend operations.
`extend_bytes`	`numeric`	The total size of relation extend operations in bytes.
`extend_time`	`double precision`	Time spent waiting for extend operations in milliseconds. (if track_io_timing is enabled and object is not wal, or if track_wal_io_timing is enabled and object is wal, otherwise zero)
`hits`	`bigint`	The number of times a desired block was found in a shared buffer.
`evictions`	`bigint`	Number of times a block has been written out from a shared or local buffer in order to make it available for another use. In context normal, this counts the number of times a block was evicted from a buffer and replaced with another block. In contexts bulkwrite, bulkread, and vacuum, this counts the number of times a block was evicted from shared buffers in order to add the shared buffer to a separate, size-limited ring buffer for use in a bulk I/O operation.
`reuses`	`bigint`	The number of times an existing buffer in a size-limited ring buffer outside of shared buffers was reused as part of an I/O operation in the bulkread, bulkwrite, or vacuum contexts.
`fsyncs`	`bigint`	Number of fsync calls. These are only tracked in context normal.
`fsync_time`	`double precision`	Time spent waiting for fsync operations in milliseconds (if track_io_timing is enabled and object is not wal, or if track_wal_io_timing is enabled and object is wal, otherwise zero)
`stats_reset`	`timestamp with time zone`	Time at which these statistics were last reset.

Columns marked "implicit" are not included in SELECT *; some early statistics views are completed from same-version source, and the extra provenance is shown in the column description.

Column evolution matrix

Hover a cell for the column type

PresentAdded / type or attribute changeRemoved

COLUMN	9.0	9.1	9.2	9.3	9.4	9.5	9.6	10	11	12	13	14	15	16	17	18	19
`backend_type`	–	–	–	–	–	–	–	–	–	–	–	–	–
`object`	–	–	–	–	–	–	–	–	–	–	–	–	–
`context`	–	–	–	–	–	–	–	–	–	–	–	–	–
`reads`	–	–	–	–	–	–	–	–	–	–	–	–	–
`read_time`	–	–	–	–	–	–	–	–	–	–	–	–	–
`writes`	–	–	–	–	–	–	–	–	–	–	–	–	–
`write_time`	–	–	–	–	–	–	–	–	–	–	–	–	–
`writebacks`	–	–	–	–	–	–	–	–	–	–	–	–	–
`writeback_time`	–	–	–	–	–	–	–	–	–	–	–	–	–
`extends`	–	–	–	–	–	–	–	–	–	–	–	–	–
`extend_time`	–	–	–	–	–	–	–	–	–	–	–	–	–
`op_bytes`	–	–	–	–	–	–	–	–	–	–	–	–	–			−	–
`hits`	–	–	–	–	–	–	–	–	–	–	–	–	–
`evictions`	–	–	–	–	–	–	–	–	–	–	–	–	–
`reuses`	–	–	–	–	–	–	–	–	–	–	–	–	–
`fsyncs`	–	–	–	–	–	–	–	–	–	–	–	–	–
`fsync_time`	–	–	–	–	–	–	–	–	–	–	–	–	–
`stats_reset`	–	–	–	–	–	–	–	–	–	–	–	–	–
`read_bytes`	–	–	–	–	–	–	–	–	–	–	–	–	–	–	–
`write_bytes`	–	–	–	–	–	–	–	–	–	–	–	–	–	–	–
`extend_bytes`	–	–	–	–	–	–	–	–	–	–	–	–	–	–	–

9.0 is the coverage baseline; a column already present in the baseline is not marked as added. The matrix aligns columns by name, so a rename appears as the old column removed and a new column added.

Evolution timeline

Changes between adjacent majors

PostgreSQL 19 ← 18

1 column description updates

PostgreSQL 18 ← 17

+ read_bytes+ write_bytes+ extend_bytes− op_bytes9 column description updatesCatalog description updated

PostgreSQL 16 ← 15Catalog added

+ backend_type+ object+ context+ reads+ read_time+ writes+ write_time+ writebacks+ writeback_time+ extends+ extend_time+ op_bytes+ hits+ evictions+ reuses+ fsyncs+ fsync_time+ stats_reset

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