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perf: optimize GetDeploymentWorkspaceAgentStats by eliminating 2nd select (#21112)

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Tracking issue here: https://github.com/coder/internal/issues/1009

To summarize, the current version of this query selects from
`workspace_agent_stats` twice. The expensive portion of this query is
the bitmap heap scan we have to do for each of these selects. We can
easily cut the cost of this query by 40-50% by cutting this down to a
single select, and using those rows for both sets of calculations.

Eliminating the heap scan itself would require a follow up PR to
introduce a new index. Blink helped with the rewrite of the query.

The current plan looks like this:
```
 Nested Loop  (cost=6101.64..6101.69 rows=1 width=64) (actual time=11.782..11.787 rows=1 loops=1)
   ->  Aggregate  (cost=2996.17..2996.19 rows=1 width=32) (actual time=3.356..3.357 rows=1 loops=1)
         ->  Bitmap Heap Scan on workspace_agent_stats  (cost=54.80..2992.86 rows=440 width=24) (actu
al time=0.346..2.927 rows=818 loops=1)
               Recheck Cond: (created_at > (now() - '00:15:00'::interval))
               Filter: (connection_median_latency_ms > '0'::double precision)
               Rows Removed by Filter: 1070
               Heap Blocks: exact=486
               ->  Bitmap Index Scan on idx_agent_stats_created_at  (cost=0.00..54.69 rows=1368 width
=0) (actual time=0.241..0.241 rows=1888 loops=1)
                     Index Cond: (created_at > (now() - '00:15:00'::interval))
   ->  Aggregate  (cost=3105.47..3105.49 rows=1 width=32) (actual time=8.418..8.420 rows=1 loops=1)
         ->  Subquery Scan on a  (cost=3060.95..3105.39 rows=7 width=32) (actual time=7.851..8.394 ro
ws=63 loops=1)
               Filter: (a.rn = 1)
               ->  WindowAgg  (cost=3060.95..3088.29 rows=1368 width=209) (actual time=7.850..8.382 r
ows=63 loops=1)
                     Run Condition: (row_number() OVER (?) <= 1)
                     ->  Sort  (cost=3060.93..3064.35 rows=1368 width=56) (actual time=7.836..8.036 r
ows=1888 loops=1)
                           Sort Key: workspace_agent_stats_1.agent_id, workspace_agent_stats_1.create
d_at DESC
                           Sort Method: quicksort  Memory: 181kB
                           ->  Bitmap Heap Scan on workspace_agent_stats workspace_agent_stats_1  (co
st=55.03..2989.67 rows=1368 width=56) (actual time=0.388..2.096 rows=1888 loops=1)
                                 Recheck Cond: (created_at > (now() - '00:15:00'::interval))
                                 Heap Blocks: exact=486
                                 ->  Bitmap Index Scan on idx_agent_stats_created_at  (cost=0.00..54.
69 rows=1368 width=0) (actual time=0.295..0.295 rows=1888 loops=1)
                                       Index Cond: (created_at > (now() - '00:15:00'::interval))
 Planning Time: 2.350 ms
 Execution Time: 13.152 ms
(24 rows)
```

The new plan looks like this
```
 Aggregate  (cost=2966.96..2966.98 rows=1 width=64) (actual time=3.812..3.814 rows=1 loops=1)
   ->  WindowAgg  (cost=2891.96..2916.94 rows=1250 width=88) (actual time=2.696..3.412 rows=1890 loop
s=1)
         ->  Sort  (cost=2891.94..2895.06 rows=1250 width=80) (actual time=2.686..2.780 rows=1890 loo
ps=1)
               Sort Key: workspace_agent_stats.agent_id, workspace_agent_stats.created_at DESC
               Sort Method: quicksort  Memory: 226kB
               ->  Bitmap Heap Scan on workspace_agent_stats  (cost=50.11..2827.64 rows=1250 width=80
) (actual time=0.218..1.551 rows=1890 loops=1)
                     Recheck Cond: (created_at > (now() - '00:15:00'::interval))
                     Heap Blocks: exact=474
                     ->  Bitmap Index Scan on idx_agent_stats_created_at  (cost=0.00..49.80 rows=1250
 width=0) (actual time=0.146..0.147 rows=1890 loops=1)
                           Index Cond: (created_at > (now() - '00:15:00'::interval))
 Planning Time: 0.534 ms
 Execution Time: 3.969 ms
(12 rows)
```

If we compare the results of the query they're similar enough that any
differences can be attributed to slightly different timestamps for
`now()` in the version of the query I am using to generate results for
comparison:
```
 workspace_rx_bytes | workspace_tx_bytes | workspace_connection_latency_50 | workspace_connection_latency_95 | session_count_vscode | session_count_ssh | session_count_jetbrains | session_count_reconnecting_pty 
--------------------+--------------------+---------------------------------+---------------------------------+----------------------+-------------------+-------------------------+--------------------------------
           15263563 |           74555854 |                          47.933 |                        250.5522 |                  239 |                59 |                       3 |                              3
(1 row)

 workspace_rx_bytes | workspace_tx_bytes | workspace_connection_latency_50 | workspace_connection_latency_95 | session_count_vscode | session_count_ssh | session_count_jetbrains | session_count_reconnecting_pty 
--------------------+--------------------+---------------------------------+---------------------------------+----------------------+-------------------+-------------------------+--------------------------------
           15295819 |           74598410 |                          47.933 |                        250.5522 |                  239 |                59 |                       3 |                              3           
```

---------

Signed-off-by: Callum Styan <callumstyan@gmail.com>
This commit is contained in:
Callum Styan
2025-12-09 15:19:55 -08:00
committed by GitHub
parent fca93438ee
commit 6abb889fab
2 changed files with 50 additions and 40 deletions
Download Patch File Download Diff File Expand all files Collapse all files
coderd/database/queries/workspaceagentstats.sql
+25 -20
View File
@@ -99,27 +99,32 @@ WHERE
);
-- name: GetDeploymentWorkspaceAgentStats :one
WITH agent_stats AS (
SELECT
coalesce(SUM(rx_bytes), 0)::bigint AS workspace_rx_bytes,
coalesce(SUM(tx_bytes), 0)::bigint AS workspace_tx_bytes,
coalesce((PERCENTILE_CONT(0.5) WITHIN GROUP (ORDER BY connection_median_latency_ms)), -1)::FLOAT AS workspace_connection_latency_50,
coalesce((PERCENTILE_CONT(0.95) WITHIN GROUP (ORDER BY connection_median_latency_ms)), -1)::FLOAT AS workspace_connection_latency_95
FROM workspace_agent_stats
-- The greater than 0 is to support legacy agents that don't report connection_median_latency_ms.
WHERE workspace_agent_stats.created_at > $1 AND connection_median_latency_ms > 0
), latest_agent_stats AS (
SELECT
coalesce(SUM(session_count_vscode), 0)::bigint AS session_count_vscode,
coalesce(SUM(session_count_ssh), 0)::bigint AS session_count_ssh,
coalesce(SUM(session_count_jetbrains), 0)::bigint AS session_count_jetbrains,
coalesce(SUM(session_count_reconnecting_pty), 0)::bigint AS session_count_reconnecting_pty
FROM (
SELECT *, ROW_NUMBER() OVER(PARTITION BY agent_id ORDER BY created_at DESC) AS rn
FROM workspace_agent_stats WHERE created_at > $1
) AS a WHERE a.rn = 1
WITH stats AS (
SELECT
agent_id,
created_at,
rx_bytes,
tx_bytes,
connection_median_latency_ms,
session_count_vscode,
session_count_ssh,
session_count_jetbrains,
session_count_reconnecting_pty,
ROW_NUMBER() OVER (PARTITION BY agent_id ORDER BY created_at DESC) AS rn
FROM workspace_agent_stats
WHERE created_at > $1
)
SELECT * FROM agent_stats, latest_agent_stats;
SELECT
coalesce(SUM(rx_bytes), 0)::bigint AS workspace_rx_bytes,
coalesce(SUM(tx_bytes), 0)::bigint AS workspace_tx_bytes,
-- The greater than 0 is to support legacy agents that don't report connection_median_latency_ms.
coalesce((PERCENTILE_CONT(0.5) WITHIN GROUP (ORDER BY connection_median_latency_ms) FILTER (WHERE connection_median_latency_ms > 0)), -1)::FLOAT AS workspace_connection_latency_50,
coalesce((PERCENTILE_CONT(0.95) WITHIN GROUP (ORDER BY connection_median_latency_ms) FILTER (WHERE connection_median_latency_ms > 0)), -1)::FLOAT AS workspace_connection_latency_95,
coalesce(SUM(session_count_vscode) FILTER (WHERE rn = 1), 0)::bigint AS session_count_vscode,
coalesce(SUM(session_count_ssh) FILTER (WHERE rn = 1), 0)::bigint AS session_count_ssh,
coalesce(SUM(session_count_jetbrains) FILTER (WHERE rn = 1), 0)::bigint AS session_count_jetbrains,
coalesce(SUM(session_count_reconnecting_pty) FILTER (WHERE rn = 1), 0)::bigint AS session_count_reconnecting_pty
FROM stats;
-- name: GetDeploymentWorkspaceAgentUsageStats :one
WITH agent_stats AS (