Horton

Re: refactoring relation extension and BufferAlloc(), faster COPY

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Alvaro Herrera <alvherre@alvh.no-ip.org>
Cc: Heikki Linnakangas <hlinnaka@iki.fi>, vignesh C <vignesh21@gmail.com>, pgsql-hackers@postgresql.org, Thomas Munro <thomas.munro@gmail.com>, Melanie Plageman <melanieplageman@gmail.com>, Yura Sokolov <y.sokolov@postgrespro.ru>, Robert Haas <robertmhaas@gmail.com>
Date: 2023-03-01T07:33:18Z
Lists: pgsql-hackers 
Hi,

On 2023-02-21 17:33:31 +0100, Alvaro Herrera wrote:
> On 2023-Feb-21, Heikki Linnakangas wrote:
> 
> > > +static BlockNumber
> > > +BulkExtendSharedRelationBuffered(Relation rel,
> > > +								 SMgrRelation smgr,
> > > +								 bool skip_extension_lock,
> > > +								 char relpersistence,
> > > +								 ForkNumber fork, ReadBufferMode mode,
> > > +								 BufferAccessStrategy strategy,
> > > +								 uint32 *num_pages,
> > > +								 uint32 num_locked_pages,
> > > +								 Buffer *buffers)
> > 
> > Ugh, that's a lot of arguments, some are inputs and some are outputs. I
> > don't have any concrete suggestions, but could we simplify this somehow?
> > Needs a comment at least.
> 
> Yeah, I noticed this too.  I think it would be easy enough to add a new
> struct that can be passed as a pointer, which can be stack-allocated
> by the caller, and which holds the input arguments that are common to
> both functions, as is sensible.

I played a fair bit with various options. I ended up not using a struct to
pass most options, but instead go for a flags argument. However, I did use a
struct for passing either relation or smgr.


typedef enum ExtendBufferedFlags {
	EB_SKIP_EXTENSION_LOCK = (1 << 0),
	EB_IN_RECOVERY = (1 << 1),
	EB_CREATE_FORK_IF_NEEDED = (1 << 2),
	EB_LOCK_FIRST = (1 << 3),

	/* internal flags follow */
	EB_RELEASE_PINS = (1 << 4),
} ExtendBufferedFlags;

/*
 * To identify the relation - either relation or smgr + relpersistence has to
 * be specified. Used via the EB_REL()/EB_SMGR() macros below. This allows us
 * to use the same function for both crash recovery and normal operation.
 */
typedef struct ExtendBufferedWhat
{
	Relation rel;
	struct SMgrRelationData *smgr;
	char relpersistence;
} ExtendBufferedWhat;

#define EB_REL(p_rel) ((ExtendBufferedWhat){.rel = p_rel})
/* requires use of EB_SKIP_EXTENSION_LOCK */
#define EB_SMGR(p_smgr, p_relpersistence) ((ExtendBufferedWhat){.smgr = p_smgr, .relpersistence = p_relpersistence})


extern Buffer ExtendBufferedRel(ExtendBufferedWhat eb,
								ForkNumber forkNum,
								BufferAccessStrategy strategy,
								uint32 flags);
extern BlockNumber ExtendBufferedRelBy(ExtendBufferedWhat eb,
									   ForkNumber fork,
									   BufferAccessStrategy strategy,
									   uint32 flags,
									   uint32 extend_by,
									   Buffer *buffers,
									   uint32 *extended_by);
extern Buffer ExtendBufferedRelTo(ExtendBufferedWhat eb,
								  ForkNumber fork,
								  BufferAccessStrategy strategy,
								  uint32 flags,
								  BlockNumber extend_to,
								  ReadBufferMode mode);

As you can see I removed ReadBufferMode from most of the functions (as
suggested by Heikki earlier). When extending by 1/multiple pages, we only need
to know whether to lock or not.

The reason ExtendBufferedRelTo() has a 'mode' argument is that that allows to
fall back to reading page normally if there was a concurrent relation
extension.

The reason EB_CREATE_FORK_IF_NEEDED exists is to remove the duplicated,
gnarly, code to do so from vm_extend(), fsm_extend().


I'm not sure about the function naming pattern. I do like 'By' a lot more than
the Bulk prefix I used before.


What do you think?


Greetings,

Andres Freund

Commits

  1. lwlock: Fix quadratic behavior with very long wait lists

  2. Support RBM_ZERO_AND_CLEANUP_LOCK in ExtendBufferedRelTo(), add tests

  3. Use ExtendBufferedRelTo() in XLogReadBufferExtended()

  4. hio: Use ExtendBufferedRelBy() to extend tables more efficiently

  5. heapam: Pass number of required pages to RelationGetBufferForTuple()

  6. Convert many uses of ReadBuffer[Extended](P_NEW) to ExtendBufferedRel()

  7. Use ExtendBufferedRelTo() in {vm,fsm}_extend()

  8. bufmgr: Introduce infrastructure for faster relation extension

  9. bufmgr: Support multiple in-progress IOs by using resowner

  10. bufmgr: Acquire and clean victim buffer separately

  11. bufmgr: Add Pin/UnpinLocalBuffer()

  12. bufmgr: Add some more error checking [infrastructure] around pinning

  13. Add smgrzeroextend(), FileZero(), FileFallocate()

  14. Don't initialize page in {vm,fsm}_extend(), not needed

  15. bufmgr: Remove buffer-write-dirty tracepoints

  16. hio: Release extension lock before initializing page / pinning VM

  17. bufmgr: Fix undefined behaviour with, unrealistically, large temp_buffers

  18. Fix memory leak and inefficiency in CREATE DATABASE ... STRATEGY WAL_LOG

  19. pgstat: Track more detailed relation IO statistics

  20. Use unnamed POSIX semaphores on Cygwin.

  21. Include RelFileLocator fields individually in BufferTag.