database/postgres
1
0
Fork 0
mirror of https://github.com/postgres/postgres.git synced 2025-07-30 11:03:19 +03:00
Code Activity

Add io_direct setting (developer-only).

Browse Source 
Provide a way to ask the kernel to use O_DIRECT (or local equivalent)
where available for data and WAL files, to avoid or minimize kernel
caching.  This hurts performance currently and is not intended for end
users yet.  Later proposed work would introduce our own I/O clustering,
read-ahead, etc to replace the facilities the kernel disables with this
option.

The only user-visible change, if the developer-only GUC is not used, is
that this commit also removes the obscure logic that would activate
O_DIRECT for the WAL when wal_sync_method=open_[data]sync and
wal_level=minimal (which also requires max_wal_senders=0).  Those are
non-default and unlikely settings, and this behavior wasn't (correctly)
documented.  The same effect can be achieved with io_direct=wal.

Author: Thomas Munro <thomas.munro@gmail.com>
Author: Andres Freund <andres@anarazel.de>
Author: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>
Reviewed-by: Justin Pryzby <pryzby@telsasoft.com>
Reviewed-by: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>
Discussion: https://postgr.es/m/CA%2BhUKGK1X532hYqJ_MzFWt0n1zt8trz980D79WbjwnT-yYLZpg%40mail.gmail.com
This commit is contained in:
Thomas Munro
2023-04-08 11:04:49 +12:00
parent faeedbcefd
commit d4e71df6d7
14 changed files with 263 additions and 35 deletions
Download Patch File Download Diff File Expand all files Collapse all files

16
src/backend/storage/buffer/bufmgr.c
View File

@ -541,8 +541,11 @@ PrefetchSharedBuffer(SMgrRelation smgr_reln,
* Try to initiate an asynchronous read. This returns false in
* recovery if the relation file doesn't exist.
*/
if (smgrprefetch(smgr_reln, forkNum, blockNum))
if ((io_direct_flags & IO_DIRECT_DATA) == 0 &&
smgrprefetch(smgr_reln, forkNum, blockNum))
{
result.initiated_io = true;
}
#endif /* USE_PREFETCH */
}
else
@ -588,11 +591,11 @@ PrefetchSharedBuffer(SMgrRelation smgr_reln,
* the kernel and therefore didn't really initiate I/O, and no way to know when
* the I/O completes other than using synchronous ReadBuffer().
*
* 3. Otherwise, the buffer wasn't already cached by PostgreSQL, and either
* 3. Otherwise, the buffer wasn't already cached by PostgreSQL, and
* USE_PREFETCH is not defined (this build doesn't support prefetching due to
* lack of a kernel facility), or the underlying relation file wasn't found and
* we are in recovery. (If the relation file wasn't found and we are not in
* recovery, an error is raised).
* lack of a kernel facility), direct I/O is enabled, or the underlying
* relation file wasn't found and we are in recovery. (If the relation file
* wasn't found and we are not in recovery, an error is raised).
*/
PrefetchBufferResult
PrefetchBuffer(Relation reln, ForkNumber forkNum, BlockNumber blockNum)
@ -5440,6 +5443,9 @@ ScheduleBufferTagForWriteback(WritebackContext *context, BufferTag *tag)
{
PendingWriteback *pending;
if (io_direct_flags & IO_DIRECT_DATA)
return;
/*
* Add buffer to the pending writeback array, unless writeback control is
* disabled.