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Introduce a maintenance_io_concurrency setting.

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Introduce a GUC and a tablespace option to control I/O prefetching, much
like effective_io_concurrency, but for work that is done on behalf of
many client sessions.

Use the new setting in heapam.c instead of the hard-coded formula
effective_io_concurrency + 10 introduced by commit 558a9165e0.  Go with
a default value of 10 for now, because it's a round number pretty close
to the value used for that existing case.

Discussion: https://postgr.es/m/CA%2BhUKGJUw08dPs_3EUcdO6M90GnjofPYrWp4YSLaBkgYwS-AqA%40mail.gmail.com
This commit is contained in:
Thomas Munro
2020-03-16 12:31:34 +13:00
parent b09ff53667
commit fc34b0d9de
12 changed files with 109 additions and 23 deletions
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16
src/backend/access/heap/heapam.c
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@ -7003,7 +7003,6 @@ heap_compute_xid_horizon_for_tuples(Relation rel,
Page hpage;
#ifdef USE_PREFETCH
XidHorizonPrefetchState prefetch_state;
int io_concurrency;
int prefetch_distance;
#endif
@ -7026,24 +7025,15 @@ heap_compute_xid_horizon_for_tuples(Relation rel,
/*
* Compute the prefetch distance that we will attempt to maintain.
*
* We don't use the regular formula to determine how much to prefetch
* here, but instead just add a constant to effective_io_concurrency.
* That's because it seems best to do some prefetching here even when
* effective_io_concurrency is set to 0, but if the DBA thinks it's OK to
* do more prefetching for other operations, then it's probably OK to do
* more prefetching in this case, too. It may be that this formula is too
* simplistic, but at the moment there is no evidence of that or any idea
* about what would work better.
*
* Since the caller holds a buffer lock somewhere in rel, we'd better make
* sure that isn't a catalog relation before we call code that does
* syscache lookups, to avoid risk of deadlock.
*/
if (IsCatalogRelation(rel))
io_concurrency = effective_io_concurrency;
prefetch_distance = maintenance_io_concurrency;
else
io_concurrency = get_tablespace_io_concurrency(rel->rd_rel->reltablespace);
prefetch_distance = Min((io_concurrency) + 10, MAX_IO_CONCURRENCY);
prefetch_distance =
get_tablespace_maintenance_io_concurrency(rel->rd_rel->reltablespace);
/* Start prefetching. */
xid_horizon_prefetch_buffer(rel, &prefetch_state, prefetch_distance);