This page describes how to monitor utilization of the columnar engine.
Verify usage of the columnar engine using EXPLAIN
To observe the new columnar operators that appear in a query's generated query
plan, you can verify the usage of the columnar engine by using the EXPLAIN statement.
EXPLAIN (ANALYZE,COSTS OFF,BUFFERS,TIMING OFF,SUMMARY OFF)
SELECT l_returnflag, l_linestatus, l_quantity, l_extendedprice,
l_discount, l_tax
FROM lineitem
WHERE l_shipdate <= date '1992-08-06'
;
QUERY PLAN
-----------------------------------------------------------------------------
Append (actual rows=3941797 loops=1)
Buffers: shared hit=9
-> Custom Scan (columnar scan) on lineitem (actual rows=3941797 loops=1)
Filter: (l_shipdate <= '1992-08-06'::date)
Rows Removed by Columnar Filter: 56054083
Columnar cache search mode: columnar filter only
Buffers: shared hit=9
-> Seq Scan on lineitem (never executed)
Filter: (l_shipdate <= '1992-08-06'::date)
Custom Scan (columnar scan)indicates that columnar-engine scanning is included in the query plan.Rows Removed by Columnar Filterlists the number of rows filtered out by the columnar vectorized execution.Columnar cache search modecan becolumnar filter only,native, orrow store scan. The planner chooses the search mode automatically based on costing and pushdown evaluation capability.
When the planner chooses the native mode, it pushes down some of the
columnar operators to the scan:
Rows Aggregated by Columnar Scanlists the number of rows that are aggregated.Rows Sorted by Columnar Scanlists the number of rows that are sorted.Rows Limited by Columnar Scanlists the limited number of rows that were scanned.
With joins, columnar scan operators can also use the Late Materialization mode.
EXPLAIN (ANALYZE,COSTS OFF,BUFFERS,TIMING OFF,SUMMARY OFF)
SELECT l_shipmode, o_orderpriority
FROM orders, lineitem
WHERE o_orderkey = l_orderkey
AND l_shipmode in ('AIR', 'FOB')
AND l_receiptdate >= date '1995-01-01'
;
QUERY PLAN
-----------------------------------------------------------------------------
Hash Join (actual rows=9865288 loops=1)
Hash Cond: (lineitem.l_orderkey = orders.o_orderkey)
Buffers: temp read=127738 written=127738
-> Append (actual rows=9865288 loops=1)
-> Custom Scan (columnar scan) on lineitem (actual rows=9865288 loops=1)
Filter: ((l_shipmode = ANY ('{AIR,FOB}'::bpchar[])) AND
(l_receiptdate >= '1995-01-01'::date))
Rows Removed by Columnar Filter: 50130592
Columnar cache search mode: native
-> Index Scan using idx_lineitem_orderkey_fkidx on lineitem
(never executed)
Filter: ((l_shipmode = ANY ('{AIR,FOB}'::bpchar[])) AND
(l_receiptdate >= '1995-01-01'::date))
-> Hash (actual rows=15000000 loops=1)
Buckets: 1048576 Batches: 32 Memory Usage: 37006kB
Buffers: temp written=83357
-> Append (actual rows=15000000 loops=1)
-> Custom Scan (columnar scan) on orders (actual rows=15000000
loops=1)
Rows Removed by Columnar Filter: 0
Columnar projection mode: late materialization
Columnar cache search mode: native
-> Seq Scan on orders (never executed)
Columnar projection mode can be late materialization.
Columnar operators choose this mode automatically when the planner optimizes
the projection by deferring the materialization of some column values.
View information about tables with columns in the column store
You can view information about the tables or the materialized views with columns
in the column store by querying the g_columnar_relations view.
SELECT * FROM g_columnar_relations; ┌─[ RECORD 1 ]────────┬───────────────────┐ │ relation_name │ tbl_parallel_test │ │ schema_name │ public │ │ database_name │ advisor │ │ status │ Usable │ │ size │ 581431259 │ │ columnar_unit_count │ 3 │ │ invalid_block_count │ 0 │ │ total_block_count │ 8337 │ ├─[ RECORD 2 ]────────┼───────────────────┤ │ relation_name │ lineitem │ │ schema_name │ public │ │ database_name │ advisor │ │ status │ Usable │ │ size │ 423224944 │ │ columnar_unit_count │ 29 │ │ invalid_block_count │ 0 │ │ total_block_count │ 115662 │ ├─[ RECORD 3 ]────────┼───────────────────┤
View information about the columns in the column store
You can view information about the columns in the column store by querying
the g_columnar_columns view, including those columns' size and the
last access time.
SELECT database_name, schema_name, relation_name, column_name, size_in_bytes, last_accessed_time FROM g_columnar_columns;
View columnar engine execution statistics for recent queries
You can view columnar engine execution statistics for recent queries using the
g_columnar_stat_statements view. This view adds columnar engine statistics to
the pg_stat_statements view provided by the pg_stat_statements extension. To
use this view, you must first enable the pg_stat_statements extension.
- Enable the
pg_stat_statementsextension:CREATE EXTENSION pg_stat_statements;
- Run the queries whose statistics you want to view.
You can do this manually, or you can let enough time pass so
that your applications run these queries with
pg_stat_statementsenabled. - Query the
g_columnar_stat_statementsandpg_stat_statementsviews. Note the following query retrieves all the columnar execution statistics including those that were collected before the extensionpg_stat_statementswas created. The10value ofuseridindicates that the statistics were collected before the extensionpg_stat_statementswas created.SELECT * FROM pg_stat_statements(TRUE) AS pg_stats FULL JOIN g_columnar_stat_statements AS g_stats ON pg_stats.userid = g_stats.user_id AND pg_stats.dbid = g_stats.db_id AND pg_stats.queryid = g_stats.query_id WHERE columnar_unit_read > 0; ┌─[ RECORD 1 ]────────┬─────────────────────────────── │ userid │ 10 │ │ dbid │ 33004 │ │ queryid │ 6779068104316758833 │ │ query │ SELECT l_returnflag, ↵│ │ │ l_linestatus, ↵│ │ │ l_quantity, ↵│ │ │ l_extendedprice, ↵│ │ │ l_discount, ↵│ │ │ l_tax ↵│ │ │FROM lineitem ↵│ │ │WHERE l_shipdate <= date $1│ │ calls │ 1 │ │ total_time │ 299.969983 │ │ min_time │ 299.969983 │ │ max_time │ 299.969983 │ │ mean_time │ 299.969983 │ │ stddev_time │ 0 │ │ rows │ 392164 │ │ shared_blks_hit │ 0 │ │ shared_blks_read │ 0 │ │ shared_blks_dirtied │ 0 │ │ shared_blks_written │ 0 │ │ local_blks_hit │ 0 │ │ local_blks_read │ 0 │ │ local_blks_dirtied │ 0 │ │ local_blks_written │ 0 │ │ temp_blks_read │ 0 │ │ temp_blks_written │ 0 │ │ blk_read_time │ 0 │ │ blk_write_time │ 0 │ │ user_id │ 10 │ │ db_id │ 33004 │ │ query_id │ 6779068104316758833 │ │ columnar_unit_read │ 29 │ │ page_read │ 115662 │ │ rows_filtered │ 0 │ │ columnar_scan_time │ 0 │ └─────────────────────┴───────────────────────────────┘
View column store memory usage
To see the amount of unused RAM available to the columnar engine, you
can query the google_columnar_engine_memory_available function. The
output integer shows the available memory in megabytes (MB).
SELECT google_columnar_engine_memory_available();
View columnar engine storage cache
To view and monitor data about the storage cache of the columnar engine, you can call the following functions:
| Function | Description |
|---|---|
google_columnar_engine_storage_cache_used |
Returns the size of the used columnar engine storage cache. |
google_columnar_engine_storage_cache_available |
Returns the size of the unused columnar engine storage cache. |
google_columnar_engine_storage_cache_total |
Returns the total amount of the configured size of storage cache for the columnar engine. |
The following shows how to query a SQL function used to view and monitor data about the storage cache of the columnar engine:
SELECT SQL_FUNCTION;
Replace SQL_FUNCTION with the name of the columnar engine storage cache function
that you want to use from the preceding table.