From 090010f2ec9b1f9ac1124dc628b89586f911b641 Mon Sep 17 00:00:00 2001
From: Teodor Sigaev <teodor@sigaev.ru>
Date: Mon, 27 Mar 2017 18:34:42 +0300
Subject: [PATCH] Improve performance of
find_tabstat_entry()/get_tabstat_entry()
Patch introduces a hash map reloid -> PgStat_TableStatus which improves
performance in case of large number of tables/partitions.
Author: Aleksander Alekseev
Reviewed-by: Andres Freund, Anastasia Lubennikova, Tels, me
https://commitfest.postgresql.org/13/1058/
---
src/backend/postmaster/pgstat.c | 139 +++++++++++++++++++++-----------
1 file changed, 93 insertions(+), 46 deletions(-)
diff --git a/src/backend/postmaster/pgstat.c b/src/backend/postmaster/pgstat.c
index 869afd4c4a5..56a8bf2d17f 100644
--- a/src/backend/postmaster/pgstat.c
+++ b/src/backend/postmaster/pgstat.c
@@ -173,6 +173,20 @@ typedef struct TabStatusArray
static TabStatusArray *pgStatTabList = NULL;
+/*
+ * pgStatTabHash entry
+ */
+typedef struct TabStatHashEntry
+{
+ Oid t_id;
+ PgStat_TableStatus* tsa_entry;
+} TabStatHashEntry;
+
+/*
+ * Hash table for O(1) t_id -> tsa_entry lookup
+ */
+static HTAB *pgStatTabHash = NULL;
+
/*
* Backends store per-function info that's waiting to be sent to the collector
* in this hash table (indexed by function OID).
@@ -840,6 +854,14 @@ pgstat_report_stat(bool force)
tsa->tsa_used = 0;
}
+ /*
+ * pgStatTabHash is outdated on this point so we have to clean it,
+ * hash_destroy() will remove hash memory context, allocated in
+ * make_sure_stat_tab_initialized()
+ */
+ hash_destroy(pgStatTabHash);
+ pgStatTabHash = NULL;
+
/*
* Send partial messages. Make sure that any pending xact commit/abort
* gets counted, even if there are no table stats to send.
@@ -1684,60 +1706,88 @@ pgstat_initstats(Relation rel)
rel->pgstat_info = get_tabstat_entry(rel_id, rel->rd_rel->relisshared);
}
+/*
+ * Make sure pgStatTabList and pgStatTabHash are initialized.
+ */
+static void
+make_sure_stat_tab_initialized()
+{
+ HASHCTL ctl;
+ MemoryContext new_ctx;
+
+ if(!pgStatTabList)
+ {
+ /* This is first time procedure is called */
+ pgStatTabList = (TabStatusArray *) MemoryContextAllocZero(TopMemoryContext,
+ sizeof(TabStatusArray));
+ }
+
+ if(pgStatTabHash)
+ return;
+
+ /* Hash table was freed or never existed. */
+
+ new_ctx = AllocSetContextCreate(
+ TopMemoryContext,
+ "PGStatLookupHashTableContext",
+ ALLOCSET_DEFAULT_SIZES);
+
+ memset(&ctl, 0, sizeof(ctl));
+ ctl.keysize = sizeof(Oid);
+ ctl.entrysize = sizeof(TabStatHashEntry);
+ ctl.hcxt = new_ctx;
+
+ pgStatTabHash = hash_create("pgstat t_id to tsa_entry lookup hash table",
+ TABSTAT_QUANTUM, &ctl, HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
+}
+
/*
* get_tabstat_entry - find or create a PgStat_TableStatus entry for rel
*/
static PgStat_TableStatus *
get_tabstat_entry(Oid rel_id, bool isshared)
{
+ TabStatHashEntry* hash_entry;
PgStat_TableStatus *entry;
TabStatusArray *tsa;
- TabStatusArray *prev_tsa;
- int i;
+ bool found;
+
+ make_sure_stat_tab_initialized();
/*
- * Search the already-used tabstat slots for this relation.
+ * Find an entry or create a new one.
*/
- prev_tsa = NULL;
- for (tsa = pgStatTabList; tsa != NULL; prev_tsa = tsa, tsa = tsa->tsa_next)
+ hash_entry = hash_search(pgStatTabHash, &rel_id, HASH_ENTER, &found);
+ if(found)
+ return hash_entry->tsa_entry;
+
+ /*
+ * `hash_entry` was just created and now we have to fill it.
+ * First make sure there is a free space in a last element of pgStatTabList.
+ */
+ tsa = pgStatTabList;
+ while(tsa->tsa_used == TABSTAT_QUANTUM)
{
- for (i = 0; i < tsa->tsa_used; i++)
+ if(tsa->tsa_next == NULL)
{
- entry = &tsa->tsa_entries[i];
- if (entry->t_id == rel_id)
- return entry;
+ tsa->tsa_next = (TabStatusArray *) MemoryContextAllocZero(TopMemoryContext,
+ sizeof(TabStatusArray));
}
- if (tsa->tsa_used < TABSTAT_QUANTUM)
- {
- /*
- * It must not be present, but we found a free slot instead. Fine,
- * let's use this one. We assume the entry was already zeroed,
- * either at creation or after last use.
- */
- entry = &tsa->tsa_entries[tsa->tsa_used++];
- entry->t_id = rel_id;
- entry->t_shared = isshared;
- return entry;
- }
+ tsa = tsa->tsa_next;
}
/*
- * We ran out of tabstat slots, so allocate more. Be sure they're zeroed.
- */
- tsa = (TabStatusArray *) MemoryContextAllocZero(TopMemoryContext,
- sizeof(TabStatusArray));
- if (prev_tsa)
- prev_tsa->tsa_next = tsa;
- else
- pgStatTabList = tsa;
-
- /*
- * Use the first entry of the new TabStatusArray.
+ * Add an entry.
*/
entry = &tsa->tsa_entries[tsa->tsa_used++];
entry->t_id = rel_id;
entry->t_shared = isshared;
+
+ /*
+ * Add a corresponding entry to pgStatTabHash.
+ */
+ hash_entry->tsa_entry = entry;
return entry;
}
@@ -1749,22 +1799,19 @@ get_tabstat_entry(Oid rel_id, bool isshared)
PgStat_TableStatus *
find_tabstat_entry(Oid rel_id)
{
- PgStat_TableStatus *entry;
- TabStatusArray *tsa;
- int i;
+ TabStatHashEntry* hash_entry;
- for (tsa = pgStatTabList; tsa != NULL; tsa = tsa->tsa_next)
- {
- for (i = 0; i < tsa->tsa_used; i++)
- {
- entry = &tsa->tsa_entries[i];
- if (entry->t_id == rel_id)
- return entry;
- }
- }
+ /*
+ * There are no entries at all.
+ */
+ if(!pgStatTabHash)
+ return NULL;
- /* Not present */
- return NULL;
+ hash_entry = hash_search(pgStatTabHash, &rel_id, HASH_FIND, NULL);
+ if(!hash_entry)
+ return NULL;
+
+ return hash_entry->tsa_entry;
}
/*
--
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