|
1 | | -#sr_plan |
| 1 | +#Save and restore query plans in PostgreSQL |
| 2 | + |
| 3 | +##Rationale |
| 4 | + |
| 5 | +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. |
| 6 | + |
| 7 | +##Build |
| 8 | + |
| 9 | +Dependencies: >= Python 3.2, Mako, pycparser |
| 10 | +If you only have a Python you can use the virtual environment: |
| 11 | +```bash |
| 12 | +virtualenv env |
| 13 | +source ./env/bin/activate |
| 14 | +pip install -r ./requirements.txt |
| 15 | +``` |
| 16 | + |
| 17 | +Then you need to generate C code and compiled it: |
| 18 | +```bash |
| 19 | +make USE_PGXS=1 genparser |
| 20 | +make USE_PGXS=1 |
| 21 | +make USE_PGXS=1 install |
| 22 | +``` |
| 23 | + |
| 24 | +and modify your postgres config: |
| 25 | +``` |
| 26 | +shared_preload_libraries = 'sr_plan.so' |
| 27 | +``` |
| 28 | + |
| 29 | +##Usage |
| 30 | +In your db: |
| 31 | +```SQL |
| 32 | +CREATE EXTENSION sr_plan; |
| 33 | +``` |
| 34 | +If you want to save the query plan is necessary to set the variable: |
| 35 | +```SQL |
| 36 | +setsr_plan.write_mode= true; |
| 37 | +``` |
| 38 | +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. |
| 39 | +Making an example query: |
| 40 | +```SQL |
| 41 | +select query_hashfrom sr_planswhere query_hash=10; |
| 42 | +``` |
| 43 | +disable saving the query: |
| 44 | +```SQL |
| 45 | +setsr_plan.write_mode= false; |
| 46 | +``` |
| 47 | +Now verify that your query is saved: |
| 48 | +```SQL |
| 49 | +select query_hash, enable, valid, query, explain_jsonb_plan(plan)from sr_plans; |
| 50 | + |
| 51 | + query_hash | enable | valid | query | explain_jsonb_plan |
| 52 | +------------+--------+-------+------------------------------------------------------+---------------------------------------------------- |
| 53 | +1783086253 | f | t |select query_hashfrom sr_planswhere query_hash=10; | Bitmap Heap Scanon sr_plans+ |
| 54 | + | | | | Recheck Cond: (query_hash=10)+ |
| 55 | + | | | |-> Bitmap Index Scanon sr_plans_query_hash_idx+ |
| 56 | + | | | | Index Cond: (query_hash=10)+ |
| 57 | + | | | | |
| 58 | + |
| 59 | +``` |
| 60 | + |
| 61 | +explain_jsonb_plan function allows you to display explain execute the plan of which lies in jsonb. By default, all the plans are off, you need enable it: |
| 62 | +```SQL |
| 63 | +update sr_plansset enable=truewhere query_hash=1783086253; |
| 64 | +``` |
| 65 | +(1783086253 for example only) |
| 66 | +After that, the plan for the query will be taken from the sr_plans. |
| 67 | + |
| 68 | +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. |
| 69 | +For the parameters we use a special function_p (anyelement) example: |
| 70 | +```SQL |
| 71 | +select query_hashfrom sr_planswhere query_hash=1000+_p(10); |
| 72 | +``` |
| 73 | +if we keep the plan for the query and enable it to be used also for the following queries: |
| 74 | +```SQL |
| 75 | +select query_hashfrom sr_planswhere query_hash=1000+_p(11); |
| 76 | +select query_hashfrom sr_planswhere query_hash=1000+_p(-5); |
| 77 | +``` |