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Posted to commits@age.apache.org by jo...@apache.org on 2022/10/14 03:43:59 UTC
[age-website] branch developer-manual updated: Initial explanation of Postgres query stages
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joshinnis pushed a commit to branch developer-manual
in repository https://gitbox.apache.org/repos/asf/age-website.git
The following commit(s) were added to refs/heads/developer-manual by this push:
new ddb6e25 Initial explanation of Postgres query stages
ddb6e25 is described below
commit ddb6e2546ad062725fa0720f3d81cd7a3a1f522a
Author: Josh Innis <Jo...@gmail.com>
AuthorDate: Fri Oct 14 12:43:11 2022 +0900
Initial explanation of Postgres query stages
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docs/postgres/query_processing.md | 39 ++++++++++++++++++++++++++++++++++++++
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@@ -7,3 +7,10 @@ Apache AGE's documentation
:maxdepth: 1
intro/overview
+
+
+.. toctree::
+ :caption: Postgres Internals
+ :maxdepth: 1
+
+ postgres/query_processing
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+# Postgres Query Processing Stages
+
+## Overview
+
+When a query is submitted to Postgres, the server will process the query in 5 stages.
+
+<img src='https://www.interdb.jp/pg/img/fig-3-01.png'>
+
+
+## Parsing
+
+The first stages is the parser stage. The purpose of this stage in to transform the query given to postgres from a string to adata structure that the rest of the system can understand.
+
+Commonly known as an <a src='https://en.wikipedia.org/wiki/Abstract_syntax_tree'>abstract syntax tree (AST)</a> this data structed will then be passed to the rest of the system for processing. This stage does no interpretation of the query and only creates the AST and verifies that the user provided a syntatically correct query.
+
+The core of the postgres phase is it's <a src='https://github.com/postgres/postgres/blob/master/src/backend/parser/gram.y'>grammar file.</a>
+
+## Transform/Analyzer
+
+Once the parser stage is complete, the analyze phase will start. The goal of this stage is to interpret what the query is trying to do. What tables are being used, is the query a SELECT, INSERT, UPDATE, or DELETE, what data the user wants returned, etc.
+
+The core of the transform phase is <a src='https://github.com/postgres/postgres/blob/master/src/backend/parser/analyze.c'>src/backend/parser/analyze.c</a>.
+
+## Optimizer/Planner
+
+The optimizer/planner can be considered two or possibly three phases combined into one.
+
+Once Postgres has figured out what the query wants to do, there is a phase where Postgres tries to optimize the query.
+
+A given SQL query can be actually executed in a wide variety of different ways, each of which will produce the same set of results. If it is computationally feasible, the query optimizer will examine each of these possible execution plans, ultimately selecting the execution plan that is expected to run the fastest.
+
+The entry point into the optimizer/planner is <a src='https://github.com/postgres/postgres/blob/master/src/backend/optimizer/plan/planner.c#L270'>here.</a>
+
+## Execution
+
+The final stage is when the query is actually executed. Once postgres has created a plan for how to execute the query, this stage will take the query and execute it.
+
+The entry point for the execution phase is <a src='https://github.com/postgres/postgres/blob/master/src/backend/executor/execMain.c'>here.</a>
+