https://github.com/postgrespro/sr_plan
Save and restore query plans in PostgreSQL
https://github.com/postgrespro/sr_plan
extension outline planning postgres postgresql
Last synced: 6 days ago
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Save and restore query plans in PostgreSQL
- Host: GitHub
- URL: https://github.com/postgrespro/sr_plan
- Owner: postgrespro
- License: other
- Created: 2015-12-30T09:45:26.000Z (over 9 years ago)
- Default Branch: master
- Last Pushed: 2022-08-01T16:48:09.000Z (over 2 years ago)
- Last Synced: 2025-04-24T10:48:43.981Z (7 days ago)
- Topics: extension, outline, planning, postgres, postgresql
- Language: C
- Size: 151 KB
- Stars: 61
- Watchers: 33
- Forks: 11
- Open Issues: 3
-
Metadata Files:
- Readme: README.md
- License: LICENSE
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# Save and restore query plans in PostgreSQL
## Rationale
sr_plan looks like Oracle Outline system. It can be used to lock the execution plan. It is necessary if you do not trust the planner or able to form a better plan.
## Build and install
```bash
make USE_PGXS=1
make USE_PGXS=1 install
```
and modify your postgres config:
```
shared_preload_libraries = 'sr_plan'
```
## Usage
Install the extension in your database:
```SQL
CREATE EXTENSION sr_plan;
```
If you want to save the query plan is necessary to set the variable:
```SQL
set sr_plan.write_mode = true;
```
Now plans for all subsequent queries will be stored in the table sr_plans.
Don't forget that all queries will be stored including duplicates.
Make an example query:
```SQL
select query_hash from sr_plans where query_hash=10;
```
Disable saving the plan for the query:
```SQL
set sr_plan.write_mode = false;
```
Enable it:
```SQL
update sr_plans set enable=true;
```
After that, the plan for the query will be taken from the sr_plans.
In addition sr plan allows you to save a parameterized query plan.
In this case, we have some constants in the query are not essential.
For the parameters we use a special function _p (anyelement) example:
```SQL
select query_hash from sr_plans where query_hash=1000+_p(10);
```
If we keep the plan for the query and enable it to be used also for the following queries:
```SQL
select query_hash from sr_plans where query_hash=1000+_p(11);
select query_hash from sr_plans where query_hash=1000+_p(-5);
```
## EXPLAIN for saved plans
It is possible to see saved plans by using `show_plan` function. It requires
knowing query hash which could be fetched from `sr_plans` table.
Examples:
Show enabled plan for query hash:
```SQL
SELECT show_plan(1);
show_plan
----------------------------------------------
("Seq Scan on public.explain_test")
(" Output: test_attr1, test_attr2")
(" Filter: (explain_test.test_attr1 = 10)")
(3 rows)
```
Get second saved plan by using `index` parameter (ignores `enable` attribute):
```SQL
SELECT show_plan(1, index := 2);
show_plan
----------------------------------------------
("Seq Scan on public.explain_test")
(" Output: test_attr1, test_attr2")
(" Filter: (explain_test.test_attr1 = 10)")
(3 rows)
```
Use another output format (supported formats are `json`, `text`, `xml`, `yaml`):
```SQL
SELECT show_plan(1, format := 'json');
show_plan
------------------------------------------------------
("[ +
{ +
""Plan"": { +
""Node Type"": ""Seq Scan"", +
""Parallel Aware"": false, +
""Relation Name"": ""explain_test"", +
""Schema"": ""public"", +
""Alias"": ""explain_test"", +
""Output"": [""test_attr1"", ""test_attr2""], +
""Filter"": ""(explain_test.test_attr1 = 10)""+
} +
} +
]")
(1 row)
```
## `pg_stat_statements` integration
`sr_plans` table contains `query_id` columns which could be used to make
joins with `pg_stat_statements` tables and views.
Note: in `shared_preload_libraries` list `pg_stat_statements` should be
specified after `sr_plan`.