Re: Early WIP/PoC for inlining CTEs

Andreas Karlsson <andreas@proxel.se>

From: Andreas Karlsson <andreas@proxel.se>

To: Robert Haas <robertmhaas@gmail.com>, Andres Freund <andres@anarazel.de>

Cc: Thomas Munro <thomas.munro@enterprisedb.com>, Andrew Gierth <andrew@tao11.riddles.org.uk>, Tom Lane <tgl@sss.pgh.pa.us>, David Fetter <david@fetter.org>, Pg Hackers <pgsql-hackers@postgresql.org>

Date: 2019-01-17T15:48:07Z

Lists: pgsql-hackers

Commits

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Prevent inlining of multiply-referenced CTEs with outer recursive refs.
- 9476131278c7 12.0 landed
Allow user control of CTE materialization, and change the default behavior.
- 608b167f9f9c 12.0 landed
Split QTW_EXAMINE_RTES flag into QTW_EXAMINE_RTES_BEFORE/_AFTER.
- 18c0da88a5d9 12.0 landed
document when PREPARE uses generic plans
- fab9d1da4a21 9.6.0 cited

On 1/11/19 8:10 PM, Robert Haas wrote:
> WITH cte_name [[NOT] MATERIALIZED] AS (query) main_query...

Hm, when would one want "NOT MATERIALIZED"? I am not sure I see the 
usefulness of forcing inlining other than if we by default do not inline 
when a CTE is referenced multiple times.

Do you imaging it working something like the below?

1. Default

# Not inlined

- Referenced multiple times
- Includes FOR UPDATE|SHARE
- Includes volatile functions
- Recurisve
- DML

# Inlined

- Simple case (no side effects, referenced once)

2. MATERIALIZED

# Not inlined

- Everything

# Inlined

- (none)

3. NOT MATERIALIZED

# Not inlined

- Recursive
- DML

# Inlined

- Everything else

Andreas