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raw | patch | inline | side by side (parent: 1f99886)
raw | patch | inline | side by side (parent: 1f99886)
| author | Nathan Bossart <nathan@postgresql.org> | |
| Tue, 19 Sep 2023 21:31:29 +0000 (14:31 -0700) | ||
| committer | Nathan Bossart <nathan@postgresql.org> | |
| Tue, 19 Sep 2023 21:31:29 +0000 (14:31 -0700) |
Presently, parallel restores spend a lot of time sorting this list
so that we pick the largest items first. With many tables, this
sorting can become a significant bottleneck. There are a couple of
reports from the field about this, and it is easy to reproduce.
This commit improves the performance of parallel pg_restore with
many tables by converting its ready_list to a priority queue, i.e.,
a binary heap. We will first try to run the highest priority item,
but if it cannot be chosen due to the lock heuristic, we'll do a
sequential scan through the heap nodes until we find one that is
runnable. This means that we might end up picking an item with a
much lower priority. However, we expect that we will typically be
able to pick one of the first few items, which should usually have
a relatively high priority.
Suggested-by: Tom Lane
Tested-by: Pierre Ducroquet
Reviewed-by: Tom Lane
Discussion: https://postgr.es/m/3612876.1689443232%40sss.pgh.pa.us
so that we pick the largest items first. With many tables, this
sorting can become a significant bottleneck. There are a couple of
reports from the field about this, and it is easy to reproduce.
This commit improves the performance of parallel pg_restore with
many tables by converting its ready_list to a priority queue, i.e.,
a binary heap. We will first try to run the highest priority item,
but if it cannot be chosen due to the lock heuristic, we'll do a
sequential scan through the heap nodes until we find one that is
runnable. This means that we might end up picking an item with a
much lower priority. However, we expect that we will typically be
able to pick one of the first few items, which should usually have
a relatively high priority.
Suggested-by: Tom Lane
Tested-by: Pierre Ducroquet
Reviewed-by: Tom Lane
Discussion: https://postgr.es/m/3612876.1689443232%40sss.pgh.pa.us
| src/bin/pg_dump/pg_backup_archiver.c | patch | blob | blame | history |
index 4d83381d84082a87baf563113233e6a2d40a6120..cc06f1c81773f6bd68853edf6ce2ac67093457e9 100644 (file)
#include "compress_io.h"
#include "dumputils.h"
#include "fe_utils/string_utils.h"
+#include "lib/binaryheap.h"
#include "lib/stringinfo.h"
#include "libpq/libpq-fs.h"
#include "parallel.h"
#define TEXT_DUMP_HEADER "--\n-- PostgreSQL database dump\n--\n\n"
#define TEXT_DUMPALL_HEADER "--\n-- PostgreSQL database cluster dump\n--\n\n"
-/*
- * State for tracking TocEntrys that are ready to process during a parallel
- * restore. (This used to be a list, and we still call it that, though now
- * it's really an array so that we can apply qsort to it.)
- *
- * tes[] is sized large enough that we can't overrun it.
- * The valid entries are indexed first_te .. last_te inclusive.
- * We periodically sort the array to bring larger-by-dataLength entries to
- * the front; "sorted" is true if the valid entries are known sorted.
- */
-typedef struct _parallelReadyList
-{
- TocEntry **tes; /* Ready-to-dump TocEntrys */
- int first_te; /* index of first valid entry in tes[] */
- int last_te; /* index of last valid entry in tes[] */
- bool sorted; /* are valid entries currently sorted? */
-} ParallelReadyList;
-
static ArchiveHandle *_allocAH(const char *FileSpec, const ArchiveFormat fmt,
const pg_compress_specification compression_spec,
static void pending_list_header_init(TocEntry *l);
static void pending_list_append(TocEntry *l, TocEntry *te);
static void pending_list_remove(TocEntry *te);
-static void ready_list_init(ParallelReadyList *ready_list, int tocCount);
-static void ready_list_free(ParallelReadyList *ready_list);
-static void ready_list_insert(ParallelReadyList *ready_list, TocEntry *te);
-static void ready_list_remove(ParallelReadyList *ready_list, int i);
-static void ready_list_sort(ParallelReadyList *ready_list);
-static int TocEntrySizeCompare(const void *p1, const void *p2);
-static void move_to_ready_list(TocEntry *pending_list,
- ParallelReadyList *ready_list,
+static int TocEntrySizeCompareQsort(const void *p1, const void *p2);
+static int TocEntrySizeCompareBinaryheap(void *p1, void *p2, void *arg);
+static void move_to_ready_heap(TocEntry *pending_list,
+ binaryheap *ready_heap,
RestorePass pass);
-static TocEntry *pop_next_work_item(ParallelReadyList *ready_list,
+static TocEntry *pop_next_work_item(binaryheap *ready_heap,
ParallelState *pstate);
static void mark_dump_job_done(ArchiveHandle *AH,
TocEntry *te,
static void repoint_table_dependencies(ArchiveHandle *AH);
static void identify_locking_dependencies(ArchiveHandle *AH, TocEntry *te);
static void reduce_dependencies(ArchiveHandle *AH, TocEntry *te,
- ParallelReadyList *ready_list);
+ binaryheap *ready_heap);
static void mark_create_done(ArchiveHandle *AH, TocEntry *te);
static void inhibit_data_for_failed_table(ArchiveHandle *AH, TocEntry *te);
}
if (ntes > 1)
- qsort(tes, ntes, sizeof(TocEntry *), TocEntrySizeCompare);
+ qsort(tes, ntes, sizeof(TocEntry *), TocEntrySizeCompareQsort);
for (int i = 0; i < ntes; i++)
DispatchJobForTocEntry(AH, pstate, tes[i], ACT_DUMP,
(void) restore_toc_entry(AH, next_work_item, false);
- /* Reduce dependencies, but don't move anything to ready_list */
+ /* Reduce dependencies, but don't move anything to ready_heap */
reduce_dependencies(AH, next_work_item, NULL);
}
else
restore_toc_entries_parallel(ArchiveHandle *AH, ParallelState *pstate,
TocEntry *pending_list)
{
- ParallelReadyList ready_list;
+ binaryheap *ready_heap;
TocEntry *next_work_item;
pg_log_debug("entering restore_toc_entries_parallel");
- /* Set up ready_list with enough room for all known TocEntrys */
- ready_list_init(&ready_list, AH->tocCount);
+ /* Set up ready_heap with enough room for all known TocEntrys */
+ ready_heap = binaryheap_allocate(AH->tocCount,
+ TocEntrySizeCompareBinaryheap,
+ NULL);
/*
* The pending_list contains all items that we need to restore. Move all
- * items that are available to process immediately into the ready_list.
+ * items that are available to process immediately into the ready_heap.
* After this setup, the pending list is everything that needs to be done
- * but is blocked by one or more dependencies, while the ready list
+ * but is blocked by one or more dependencies, while the ready heap
* contains items that have no remaining dependencies and are OK to
* process in the current restore pass.
*/
AH->restorePass = RESTORE_PASS_MAIN;
- move_to_ready_list(pending_list, &ready_list, AH->restorePass);
+ move_to_ready_heap(pending_list, ready_heap, AH->restorePass);
/*
* main parent loop
for (;;)
{
/* Look for an item ready to be dispatched to a worker */
- next_work_item = pop_next_work_item(&ready_list, pstate);
+ next_work_item = pop_next_work_item(ready_heap, pstate);
if (next_work_item != NULL)
{
/* If not to be restored, don't waste time launching a worker */
next_work_item->dumpId,
next_work_item->desc, next_work_item->tag);
/* Update its dependencies as though we'd completed it */
- reduce_dependencies(AH, next_work_item, &ready_list);
+ reduce_dependencies(AH, next_work_item, ready_heap);
/* Loop around to see if anything else can be dispatched */
continue;
}
/* Dispatch to some worker */
DispatchJobForTocEntry(AH, pstate, next_work_item, ACT_RESTORE,
- mark_restore_job_done, &ready_list);
+ mark_restore_job_done, ready_heap);
}
else if (IsEveryWorkerIdle(pstate))
{
/* Advance to next restore pass */
AH->restorePass++;
/* That probably allows some stuff to be made ready */
- move_to_ready_list(pending_list, &ready_list, AH->restorePass);
+ move_to_ready_heap(pending_list, ready_heap, AH->restorePass);
/* Loop around to see if anything's now ready */
continue;
}
next_work_item ? WFW_ONE_IDLE : WFW_GOT_STATUS);
}
- /* There should now be nothing in ready_list. */
- Assert(ready_list.first_te > ready_list.last_te);
+ /* There should now be nothing in ready_heap. */
+ Assert(binaryheap_empty(ready_heap));
- ready_list_free(&ready_list);
+ binaryheap_free(ready_heap);
pg_log_info("finished main parallel loop");
}
}
-/*
- * Initialize the ready_list with enough room for up to tocCount entries.
- */
-static void
-ready_list_init(ParallelReadyList *ready_list, int tocCount)
-{
- ready_list->tes = (TocEntry **)
- pg_malloc(tocCount * sizeof(TocEntry *));
- ready_list->first_te = 0;
- ready_list->last_te = -1;
- ready_list->sorted = false;
-}
-
-/*
- * Free storage for a ready_list.
- */
-static void
-ready_list_free(ParallelReadyList *ready_list)
-{
- pg_free(ready_list->tes);
-}
-
-/* Add te to the ready_list */
-static void
-ready_list_insert(ParallelReadyList *ready_list, TocEntry *te)
-{
- ready_list->tes[++ready_list->last_te] = te;
- /* List is (probably) not sorted anymore. */
- ready_list->sorted = false;
-}
-
-/* Remove the i'th entry in the ready_list */
-static void
-ready_list_remove(ParallelReadyList *ready_list, int i)
-{
- int f = ready_list->first_te;
-
- Assert(i >= f && i <= ready_list->last_te);
-
- /*
- * In the typical case where the item to be removed is the first ready
- * entry, we need only increment first_te to remove it. Otherwise, move
- * the entries before it to compact the list. (This preserves sortedness,
- * if any.) We could alternatively move the entries after i, but there
- * are typically many more of those.
- */
- if (i > f)
- {
- TocEntry **first_te_ptr = &ready_list->tes[f];
-
- memmove(first_te_ptr + 1, first_te_ptr, (i - f) * sizeof(TocEntry *));
- }
- ready_list->first_te++;
-}
-
-/* Sort the ready_list into the desired order */
-static void
-ready_list_sort(ParallelReadyList *ready_list)
-{
- if (!ready_list->sorted)
- {
- int n = ready_list->last_te - ready_list->first_te + 1;
-
- if (n > 1)
- qsort(ready_list->tes + ready_list->first_te, n,
- sizeof(TocEntry *),
- TocEntrySizeCompare);
- ready_list->sorted = true;
- }
-}
-
/* qsort comparator for sorting TocEntries by dataLength */
static int
-TocEntrySizeCompare(const void *p1, const void *p2)
+TocEntrySizeCompareQsort(const void *p1, const void *p2)
{
const TocEntry *te1 = *(const TocEntry *const *) p1;
const TocEntry *te2 = *(const TocEntry *const *) p2;
return 0;
}
+/* binaryheap comparator for sorting TocEntries by dataLength */
+static int
+TocEntrySizeCompareBinaryheap(void *p1, void *p2, void *arg)
+{
+ /* return opposite of qsort comparator for max-heap */
+ return -TocEntrySizeCompareQsort(&p1, &p2);
+}
+
/*
- * Move all immediately-ready items from pending_list to ready_list.
+ * Move all immediately-ready items from pending_list to ready_heap.
*
* Items are considered ready if they have no remaining dependencies and
* they belong in the current restore pass. (See also reduce_dependencies,
* which applies the same logic one-at-a-time.)
*/
static void
-move_to_ready_list(TocEntry *pending_list,
- ParallelReadyList *ready_list,
+move_to_ready_heap(TocEntry *pending_list,
+ binaryheap *ready_heap,
RestorePass pass)
{
TocEntry *te;
{
/* Remove it from pending_list ... */
pending_list_remove(te);
- /* ... and add to ready_list */
- ready_list_insert(ready_list, te);
+ /* ... and add to ready_heap */
+ binaryheap_add(ready_heap, te);
}
}
}
/*
* Find the next work item (if any) that is capable of being run now,
- * and remove it from the ready_list.
+ * and remove it from the ready_heap.
*
* Returns the item, or NULL if nothing is runnable.
*
* To qualify, the item must have no remaining dependencies
* and no requirements for locks that are incompatible with
- * items currently running. Items in the ready_list are known to have
+ * items currently running. Items in the ready_heap are known to have
* no remaining dependencies, but we have to check for lock conflicts.
*/
static TocEntry *
-pop_next_work_item(ParallelReadyList *ready_list,
+pop_next_work_item(binaryheap *ready_heap,
ParallelState *pstate)
{
/*
- * Sort the ready_list so that we'll tackle larger jobs first.
- */
- ready_list_sort(ready_list);
-
- /*
- * Search the ready_list until we find a suitable item.
+ * Search the ready_heap until we find a suitable item. Note that we do a
+ * sequential scan through the heap nodes, so even though we will first
+ * try to choose the highest-priority item, we might end up picking
+ * something with a much lower priority. However, we expect that we will
+ * typically be able to pick one of the first few items, which should
+ * usually have a relatively high priority.
*/
- for (int i = ready_list->first_te; i <= ready_list->last_te; i++)
+ for (int i = 0; i < binaryheap_size(ready_heap); i++)
{
- TocEntry *te = ready_list->tes[i];
+ TocEntry *te = (TocEntry *) binaryheap_get_node(ready_heap, i);
bool conflicts = false;
/*
continue;
/* passed all tests, so this item can run */
- ready_list_remove(ready_list, i);
+ binaryheap_remove_node(ready_heap, i);
return te;
}
int status,
void *callback_data)
{
- ParallelReadyList *ready_list = (ParallelReadyList *) callback_data;
+ binaryheap *ready_heap = (binaryheap *) callback_data;
pg_log_info("finished item %d %s %s",
te->dumpId, te->desc, te->tag);
pg_fatal("worker process failed: exit code %d",
status);
- reduce_dependencies(AH, te, ready_list);
+ reduce_dependencies(AH, te, ready_heap);
}
/*
* Remove the specified TOC entry from the depCounts of items that depend on
* it, thereby possibly making them ready-to-run. Any pending item that
- * becomes ready should be moved to the ready_list, if that's provided.
+ * becomes ready should be moved to the ready_heap, if that's provided.
*/
static void
reduce_dependencies(ArchiveHandle *AH, TocEntry *te,
- ParallelReadyList *ready_list)
+ binaryheap *ready_heap)
{
int i;
* the current restore pass, and it is currently a member of the
* pending list (that check is needed to prevent double restore in
* some cases where a list-file forces out-of-order restoring).
- * However, if ready_list == NULL then caller doesn't want any list
+ * However, if ready_heap == NULL then caller doesn't want any list
* memberships changed.
*/
if (otherte->depCount == 0 &&
_tocEntryRestorePass(otherte) == AH->restorePass &&
otherte->pending_prev != NULL &&
- ready_list != NULL)
+ ready_heap != NULL)
{
/* Remove it from pending list ... */
pending_list_remove(otherte);
- /* ... and add to ready_list */
- ready_list_insert(ready_list, otherte);
+ /* ... and add to ready_heap */
+ binaryheap_add(ready_heap, otherte);
}
}
}