mirrors/postgres
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

Standardize "read-ahead advice" terminology.

Browse Source 
Commit 6654bb920 added macOS's equivalent of POSIX_FADV_WILLNEED, and
changed some explicit references to posix_fadvise to use this more
general name for the concept.  Update some remaining references.

Reviewed-by: Peter Eisentraut <peter@eisentraut.org>
Discussion: https://postgr.es/m/0827edec-1317-4917-a186-035eb1e3241d%40eisentraut.org
This commit is contained in:
Thomas Munro 2024-09-04 10:12:20 +12:00
parent 1c61fd8b52
commit 813fde73d4
2 changed files with 9 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
src/backend/access/transam/xlogprefetcher.c
View File

@ -1083,7 +1083,7 @@ check_recovery_prefetch(int *new_value, void **extra, GucSource source)
#ifndef USE_PREFETCH
if (*new_value == RECOVERY_PREFETCH_ON)
{
GUC_check_errdetail("\"recovery_prefetch\" is not supported on platforms that lack posix_fadvise().");
GUC_check_errdetail("\"recovery_prefetch\" is not supported on platforms that lack support for issuing read-ahead advice.");
return false;
}
#endif

15
src/backend/storage/aio/read_stream.c
View File

@ -24,16 +24,17 @@
* already. There is no benefit to looking ahead more than one block, so
* distance is 1. This is the default initial assumption.
*
* B) I/O is necessary, but fadvise is undesirable because the access is
* sequential, or impossible because direct I/O is enabled or the system
* doesn't support fadvise. There is no benefit in looking ahead more than
* B) I/O is necessary, but read-ahead advice is undesirable because the
* access is sequential and we can rely on the kernel's read-ahead heuristics,
* or impossible because direct I/O is enabled, or the system doesn't support
* read-ahead advice. There is no benefit in looking ahead more than
* io_combine_limit, because in this case the only goal is larger read system
* calls. Looking further ahead would pin many buffers and perform
* speculative work looking ahead for no benefit.
* speculative work for no benefit.
*
* C) I/O is necessary, it appears random, and this system supports fadvise.
* We'll look further ahead in order to reach the configured level of I/O
* concurrency.
* C) I/O is necessary, it appears to be random, and this system supports
* read-ahead advice. We'll look further ahead in order to reach the
* configured level of I/O concurrency.
*
* The distance increases rapidly and decays slowly, so that it moves towards
* those levels as different I/O patterns are discovered. For example, a