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Commit090010f

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Improve performance of find_tabstat_entry()/get_tabstat_entry()
Patch introduces a hash map reloid -> PgStat_TableStatus which improvesperformance in case of large number of tables/partitions.Author: Aleksander AlekseevReviewed-by: Andres Freund, Anastasia Lubennikova, Tels, mehttps://commitfest.postgresql.org/13/1058/
1 parentd655614 commit090010f

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1 file changed

+93
-46
lines changed

1 file changed

+93
-46
lines changed

‎src/backend/postmaster/pgstat.c

Lines changed: 93 additions & 46 deletions
Original file line numberDiff line numberDiff line change
@@ -173,6 +173,20 @@ typedef struct TabStatusArray
173173

174174
staticTabStatusArray*pgStatTabList=NULL;
175175

176+
/*
177+
* pgStatTabHash entry
178+
*/
179+
typedefstructTabStatHashEntry
180+
{
181+
Oidt_id;
182+
PgStat_TableStatus*tsa_entry;
183+
}TabStatHashEntry;
184+
185+
/*
186+
* Hash table for O(1) t_id -> tsa_entry lookup
187+
*/
188+
staticHTAB*pgStatTabHash=NULL;
189+
176190
/*
177191
* Backends store per-function info that's waiting to be sent to the collector
178192
* in this hash table (indexed by function OID).
@@ -840,6 +854,14 @@ pgstat_report_stat(bool force)
840854
tsa->tsa_used=0;
841855
}
842856

857+
/*
858+
* pgStatTabHash is outdated on this point so we have to clean it,
859+
* hash_destroy() will remove hash memory context, allocated in
860+
* make_sure_stat_tab_initialized()
861+
*/
862+
hash_destroy(pgStatTabHash);
863+
pgStatTabHash=NULL;
864+
843865
/*
844866
* Send partial messages. Make sure that any pending xact commit/abort
845867
* gets counted, even if there are no table stats to send.
@@ -1684,60 +1706,88 @@ pgstat_initstats(Relation rel)
16841706
rel->pgstat_info=get_tabstat_entry(rel_id,rel->rd_rel->relisshared);
16851707
}
16861708

1709+
/*
1710+
* Make sure pgStatTabList and pgStatTabHash are initialized.
1711+
*/
1712+
staticvoid
1713+
make_sure_stat_tab_initialized()
1714+
{
1715+
HASHCTLctl;
1716+
MemoryContextnew_ctx;
1717+
1718+
if(!pgStatTabList)
1719+
{
1720+
/* This is first time procedure is called */
1721+
pgStatTabList= (TabStatusArray*)MemoryContextAllocZero(TopMemoryContext,
1722+
sizeof(TabStatusArray));
1723+
}
1724+
1725+
if(pgStatTabHash)
1726+
return;
1727+
1728+
/* Hash table was freed or never existed. */
1729+
1730+
new_ctx=AllocSetContextCreate(
1731+
TopMemoryContext,
1732+
"PGStatLookupHashTableContext",
1733+
ALLOCSET_DEFAULT_SIZES);
1734+
1735+
memset(&ctl,0,sizeof(ctl));
1736+
ctl.keysize=sizeof(Oid);
1737+
ctl.entrysize=sizeof(TabStatHashEntry);
1738+
ctl.hcxt=new_ctx;
1739+
1740+
pgStatTabHash=hash_create("pgstat t_id to tsa_entry lookup hash table",
1741+
TABSTAT_QUANTUM,&ctl,HASH_ELEM |HASH_BLOBS |HASH_CONTEXT);
1742+
}
1743+
16871744
/*
16881745
* get_tabstat_entry - find or create a PgStat_TableStatus entry for rel
16891746
*/
16901747
staticPgStat_TableStatus*
16911748
get_tabstat_entry(Oidrel_id,boolisshared)
16921749
{
1750+
TabStatHashEntry*hash_entry;
16931751
PgStat_TableStatus*entry;
16941752
TabStatusArray*tsa;
1695-
TabStatusArray*prev_tsa;
1696-
inti;
1753+
boolfound;
1754+
1755+
make_sure_stat_tab_initialized();
16971756

16981757
/*
1699-
*Search the already-used tabstat slots for this relation.
1758+
*Find an entry or create a new one.
17001759
*/
1701-
prev_tsa=NULL;
1702-
for (tsa=pgStatTabList;tsa!=NULL;prev_tsa=tsa,tsa=tsa->tsa_next)
1760+
hash_entry=hash_search(pgStatTabHash,&rel_id,HASH_ENTER,&found);
1761+
if(found)
1762+
returnhash_entry->tsa_entry;
1763+
1764+
/*
1765+
* `hash_entry` was just created and now we have to fill it.
1766+
* First make sure there is a free space in a last element of pgStatTabList.
1767+
*/
1768+
tsa=pgStatTabList;
1769+
while(tsa->tsa_used==TABSTAT_QUANTUM)
17031770
{
1704-
for (i=0;i<tsa->tsa_used;i++)
1771+
if(tsa->tsa_next==NULL)
17051772
{
1706-
entry=&tsa->tsa_entries[i];
1707-
if (entry->t_id==rel_id)
1708-
returnentry;
1773+
tsa->tsa_next= (TabStatusArray*)MemoryContextAllocZero(TopMemoryContext,
1774+
sizeof(TabStatusArray));
17091775
}
17101776

1711-
if (tsa->tsa_used<TABSTAT_QUANTUM)
1712-
{
1713-
/*
1714-
* It must not be present, but we found a free slot instead. Fine,
1715-
* let's use this one. We assume the entry was already zeroed,
1716-
* either at creation or after last use.
1717-
*/
1718-
entry=&tsa->tsa_entries[tsa->tsa_used++];
1719-
entry->t_id=rel_id;
1720-
entry->t_shared=isshared;
1721-
returnentry;
1722-
}
1777+
tsa=tsa->tsa_next;
17231778
}
17241779

17251780
/*
1726-
* We ran out of tabstat slots, so allocate more. Be sure they're zeroed.
1727-
*/
1728-
tsa= (TabStatusArray*)MemoryContextAllocZero(TopMemoryContext,
1729-
sizeof(TabStatusArray));
1730-
if (prev_tsa)
1731-
prev_tsa->tsa_next=tsa;
1732-
else
1733-
pgStatTabList=tsa;
1734-
1735-
/*
1736-
* Use the first entry of the new TabStatusArray.
1781+
* Add an entry.
17371782
*/
17381783
entry=&tsa->tsa_entries[tsa->tsa_used++];
17391784
entry->t_id=rel_id;
17401785
entry->t_shared=isshared;
1786+
1787+
/*
1788+
* Add a corresponding entry to pgStatTabHash.
1789+
*/
1790+
hash_entry->tsa_entry=entry;
17411791
returnentry;
17421792
}
17431793

@@ -1749,22 +1799,19 @@ get_tabstat_entry(Oid rel_id, bool isshared)
17491799
PgStat_TableStatus*
17501800
find_tabstat_entry(Oidrel_id)
17511801
{
1752-
PgStat_TableStatus*entry;
1753-
TabStatusArray*tsa;
1754-
inti;
1802+
TabStatHashEntry*hash_entry;
17551803

1756-
for (tsa=pgStatTabList;tsa!=NULL;tsa=tsa->tsa_next)
1757-
{
1758-
for (i=0;i<tsa->tsa_used;i++)
1759-
{
1760-
entry=&tsa->tsa_entries[i];
1761-
if (entry->t_id==rel_id)
1762-
returnentry;
1763-
}
1764-
}
1804+
/*
1805+
* There are no entries at all.
1806+
*/
1807+
if(!pgStatTabHash)
1808+
returnNULL;
17651809

1766-
/* Not present */
1767-
returnNULL;
1810+
hash_entry=hash_search(pgStatTabHash,&rel_id,HASH_FIND,NULL);
1811+
if(!hash_entry)
1812+
returnNULL;
1813+
1814+
returnhash_entry->tsa_entry;
17681815
}
17691816

17701817
/*

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