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Doc: Review for "Optionally prefetch referenced data in recovery."

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Typos, corrections and language improvements in the docs, and a few in
code comments too.

Reported-by: Justin Pryzby <pryzby@telsasoft.com>
Discussion: https://postgr.es/m/20210409033703.GP6592%40telsasoft.com
This commit is contained in:
Thomas Munro
2021-04-10 08:09:30 +12:00
parent 49fb4e6b24
commit dc88460c24
4 changed files with 10 additions and 10 deletions
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12
src/backend/access/transam/xlogprefetch.c
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@ -31,12 +31,14 @@
* stall; this is counted with "skip_fpw".
*
* The only way we currently have to know that an I/O initiated with
* PrefetchSharedBuffer() has that recovery will eventually call ReadBuffer(),
* and perform a synchronous read. Therefore, we track the number of
* PrefetchSharedBuffer() has completed is to wait for the corresponding call
* to XLogReadBufferInRedo() to return. Therefore, we track the number of
* potentially in-flight I/Os by using a circular buffer of LSNs. When it's
* full, we have to wait for recovery to replay records so that the queue
* depth can be reduced, before we can do any more prefetching. Ideally, this
* keeps us the right distance ahead to respect maintenance_io_concurrency.
* full, we have to wait for recovery to replay enough records to remove some
* LSNs, and only then can we initiate more prefetching. Ideally, this keeps
* us just the right distance ahead to respect maintenance_io_concurrency,
* though in practice it errs on the side of being too conservative because
* many I/Os complete sooner than we know.
*
*-------------------------------------------------------------------------
*/

2
src/backend/utils/misc/guc.c
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@ -2774,7 +2774,7 @@ static struct config_int ConfigureNamesInt[] =
{
{"wal_decode_buffer_size", PGC_POSTMASTER, WAL_ARCHIVE_RECOVERY,
gettext_noop("Maximum buffer size for reading ahead in the WAL during recovery."),
gettext_noop("This controls the maximum distance we can read ahead n the WAL to prefetch referenced blocks."),
gettext_noop("This controls the maximum distance we can read ahead in the WAL to prefetch referenced blocks."),
GUC_UNIT_BYTE
},
&wal_decode_buffer_size,