pg_stat_io

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.

English manual coverage begins with PostgreSQL 7.4. Source history and runtime observations have their own recorded version boundaries.

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kind: statistics
lang: en
measured attributes: true
metadata release: 18.6
runtime columns: backend_type, object, context, reads, read_bytes, read_time, writes, write_bytes, write_time, writebacks, writeback_time, extends, extend_bytes, extend_time, hits, evictions, reuses, fsyncs, fsync_time, stats_reset
runtime verified: false
source: english-manual

Definition PG 18

Catalog columns

Column	Type	Nullability	Description
backend_type	text	Nullable	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	Nullable	Target object of an I/O operation. Possible values are: relation: Permanent relations. temp relation: Temporary relations. wal: Write Ahead Logs.
context	text	Nullable	The context of an I/O operation. Possible values are: normal: The default or standard context for a type of I/O operation. For example, by default, relation data is read into and written out from shared buffers. Thus, reads and writes of relation data to and from shared buffers are tracked in context normal. init: I/O operations performed while creating the WAL segments are tracked in context init. vacuum: I/O operations performed outside of shared buffers while vacuuming and analyzing permanent relations. Temporary table vacuums use the same local buffer pool as other temporary table I/O operations and are tracked in context normal. bulkread: Certain large read I/O operations done outside of shared buffers, for example, a sequential scan of a large table. bulkwrite: Certain large write I/O operations done outside of shared buffers, such as COPY.
reads	bigint	Nullable	Number of read operations.
read_bytes	numeric	Nullable	The total size of read operations in bytes.
read_time	double precision	Nullable	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	Nullable	Number of write operations.
write_bytes	numeric	Nullable	The total size of write operations in bytes.
write_time	double precision	Nullable	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	Nullable	Number of units of size BLCKSZ (typically 8kB) which the process requested the kernel write out to permanent storage.
writeback_time	double precision	Nullable	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	Nullable	Number of relation extend operations.
extend_bytes	numeric	Nullable	The total size of relation extend operations in bytes.
extend_time	double precision	Nullable	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	Nullable	The number of times a desired block was found in a shared buffer.
evictions	bigint	Nullable	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	Nullable	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	Nullable	Number of fsync calls. These are only tracked in context normal.
fsync_time	double precision	Nullable	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	Nullable	Time at which these statistics were last reset.

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Source references

Original manual reference

Full definition and evidence JSON

Definition sources

center · PostgreSQL 18 · catalog-bilingual-repair:d0f1c7940dd0dc24597e9c48c2302f4f2c84a4a3532a9fa7f427ff26705f5c74

Text language: en · catalog-bilingual-repair:d0f1c7940dd0dc24597e9c48c2302f4f2c84a4a3532a9fa7f427ff26705f5c74