Horton

Re: executor relation handling

David Rowley <david.rowley@2ndquadrant.com>

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From: David Rowley <david.rowley@2ndquadrant.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Alvaro Herrera <alvherre@2ndquadrant.com>, Amit Langote <Langote_Amit_f8@lab.ntt.co.jp>, Jesper Pedersen <jesper.pedersen@redhat.com>, Amit Langote <amitlangote09@gmail.com>, Pg Hackers <pgsql-hackers@postgresql.org>
Date: 2018-09-30T22:54:27Z
Lists: pgsql-hackers 
On 1 October 2018 at 06:18, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> It occurred to me that it'd be reasonable to insist that the caller
> holds a lock *at least as strong* as the one being recorded in the RTE,
> and that there's also been discussions about verifying that some lock
> is held when something like heap_open(foo, NoLock) is attempted.
> So I dusted off the part of 0001 that did that, producing the
> attached delta patch.

My imagination struggles to think of a case, but perhaps one day in
the future we might have a lock manager that coordinates locks on
multiple nodes. If so, is there not a risk that one day we might have
a lock level greater than AccessExclusiveLock, meaning the following
would get broken:

+ for (slockmode = lockmode + 1;
+ slockmode <= AccessExclusiveLock;
+ slockmode++)

For index strategies we do:

#define BTGreaterStrategyNumber 5

#define BTMaxStrategyNumber 5

So would it not be better to add the following to lockdefs.h?

#define MaxLockLevel 8

then use that to terminate the loop.

-- 
 David Rowley                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services

Commits

  1. Avoid O(N^2) cost in ExecFindRowMark().

  2. Remove some unnecessary fields from Plan trees.

  3. Restore sane locking behavior during parallel query.

  4. Remove more redundant relation locking during executor startup.

  5. In the executor, use an array of pointers to access the rangetable.

  6. Centralize executor's opening/closing of Relations for rangetable entries.

  7. Change executor to just Assert that table locks were already obtained.

  8. Change rewriter/planner/executor/plancache to depend on RTE rellockmode.

  9. Add assertions that we hold some relevant lock during relation open.

  10. Create an RTE field to record the query's lock mode for each relation.