Did we want to apply this? ---------------------------------------------------------------------------
On Wed, Nov 23, 2011 at 07:33:18PM +0000, Simon Riggs wrote: > On Wed, Nov 23, 2011 at 6:15 PM, Tom Lane <t...@sss.pgh.pa.us> wrote: > > >> The real question is do we favour HOT cleanup on those small 8 tables, > >> or do we favour HOT cleanup of every other table? > > > > No, the real question is why not think a little harder and see if we can > > come up with a solution that doesn't involve making some cases worse to > > make others better. > > Slightly modified patch attached. > > When we access a shared relation and the page is prunable we re-derive > the cutoff value using GetOldestXmin. > > That code path is rarely taken. In particular, pg_shdepend is only > accessed during object creation/alter/drop, so this isn't a path we > can't spare a small amount little extra on, just like the trade-off > we've taken to make locking faster for DML while making DDL a little > slower. > > If this is still unacceptable, then I'll have to look at reducing > impact on pg_shdepend from temp tables - which is still a plan. > > -- > Simon Riggs http://www.2ndQuadrant.com/ > PostgreSQL Development, 24x7 Support, Training & Services > diff --git a/src/backend/access/heap/pruneheap.c > b/src/backend/access/heap/pruneheap.c > index 61f2ce4..5feaedc 100644 > --- a/src/backend/access/heap/pruneheap.c > +++ b/src/backend/access/heap/pruneheap.c > @@ -16,13 +16,13 @@ > > #include "access/heapam.h" > #include "access/transam.h" > +#include "catalog/catalog.h" > #include "miscadmin.h" > #include "pgstat.h" > #include "storage/bufmgr.h" > #include "utils/rel.h" > #include "utils/tqual.h" > > - > /* Working data for heap_page_prune and subroutines */ > typedef struct > { > @@ -72,6 +72,7 @@ heap_page_prune_opt(Relation relation, Buffer buffer, > TransactionId OldestXmin) > { > Page page = BufferGetPage(buffer); > Size minfree; > + Transactionid CutoffXmin = OldestXmin; > > /* > * Let's see if we really need pruning. > @@ -91,6 +92,18 @@ heap_page_prune_opt(Relation relation, Buffer buffer, > TransactionId OldestXmin) > return; > > /* > + * We choose to set RecentGlobalXmin only for the current database, > which > + * means we cannot use it to prune shared relations when reading them > with > + * MVCC snapshots. By making that choice it allows our snapshots to be > + * smaller and faster, and the RecentGlobalXmin will be further forward > + * and offer better pruning of non-shared relations. So when accessing a > + * shared relation and we see the page is prunable (above) we get an > + * OldestXmin across all databases. > + */ > + if (IsSharedRelation(relation->rd_id)) > + CutoffXmin = GetOldestXmin(true, true); > + > + /* > * We prune when a previous UPDATE failed to find enough space on the > page > * for a new tuple version, or when free space falls below the > relation's > * fill-factor target (but not less than 10%). > @@ -124,7 +137,7 @@ heap_page_prune_opt(Relation relation, Buffer buffer, > TransactionId OldestXmin) > > * needed */ > > /* OK to prune */ > - (void) heap_page_prune(relation, buffer, OldestXmin, > true, &ignore); > + (void) heap_page_prune(relation, buffer, CutoffXmin, > true, &ignore); > } > > /* And release buffer lock */ > diff --git a/src/backend/storage/ipc/procarray.c > b/src/backend/storage/ipc/procarray.c > index 1a48485..60153f4 100644 > --- a/src/backend/storage/ipc/procarray.c > +++ b/src/backend/storage/ipc/procarray.c > @@ -55,6 +55,7 @@ > #include "storage/spin.h" > #include "utils/builtins.h" > #include "utils/snapmgr.h" > +#include "utils/tqual.h" > > > /* Our shared memory area */ > @@ -1185,6 +1186,8 @@ GetMaxSnapshotSubxidCount(void) > * RecentGlobalXmin: the global xmin (oldest TransactionXmin > across all > * running transactions, except those running LAZY > VACUUM). This is > * the same computation done by GetOldestXmin(true, true). > + * For MVCC snapshots we examine transactions running only > in our > + * database, ignoring longer running transactions in other > databases. > * > * Note: this function should probably not be called with an argument that's > * not statically allocated (see xip allocation below). > @@ -1200,9 +1203,12 @@ GetSnapshotData(Snapshot snapshot) > int count = 0; > int subcount = 0; > bool suboverflowed = false; > + bool allDbs = false; > > Assert(snapshot != NULL); > > + allDbs = !IsMVCCSnapshot(snapshot); > + > /* > * Allocating space for maxProcs xids is usually overkill; numProcs > would > * be sufficient. But it seems better to do the malloc while not > holding > @@ -1278,6 +1284,12 @@ GetSnapshotData(Snapshot snapshot) > if (proc->vacuumFlags & PROC_IN_VACUUM) > continue; > > + /* MVCC snapshots ignore other databases */ > + if (!allDbs && > + proc->databaseId != MyDatabaseId && > + proc->databaseId != 0) /* always > include WalSender */ > + continue; > + > /* Update globalxmin to be the smallest valid xmin */ > xid = proc->xmin; /* fetch just once */ > if (TransactionIdIsNormal(xid) && > > -- > Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) > To make changes to your subscription: > http://www.postgresql.org/mailpref/pgsql-hackers -- Bruce Momjian <br...@momjian.us> http://momjian.us EnterpriseDB http://enterprisedb.com + It's impossible for everything to be true. + -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
