VERSION 2, with all changed made as requested to date.
As discussed on -hackers, its possible to avoid writing any WAL at all
for COPY in these circumstances:
http://archives.postgresql.org/pgsql-hackers/2006-10/msg01172.php
and again recently.
BEGIN;
CREATE TABLE foo..
COPY foo...
COMMIT;
BEGIN;
TRUNCATE foo..
COPY foo...
COMMIT;
The enclosed patch implements this, as discussed. There is no user
interface to enable/disable, just as with CTAS and CREATE INDEX; no
docs, just code comments.
This plays nicely with the --single-transaction option in psql to allow
fast restores/upgrades.
YMMV but disk bound COPY will benefit greatly from this patch, some
tests showing 100% gain. COPY is still *very* CPU intensive, so some
tests have shown negligible benefit, fyi, but that isn't the typical
case.
While testing this, I realised something: small COPY commands get no
benefit at all, but larger ones do. When we do a small normal COPY the
data stays in cache, but the WAL is written to disk and fsynced. When we
do a small fast COPY, no WAL is written, but the data is written to disk
and fsynced. With COPY, WAL and data are roughly same size, hence no I/O
benefit. With larger COPY statements, benefit is very substantial.
Applies cleanly to CVS HEAD, passes make check.
I enclose a test case that shows whether the test has succeeded by
reading the WAL Insert pointer before/after each COPY. This has been
written in such a way that we could, if we wanted to, include a new
regression test for this. There is a function that returns an immutable
value if the test passes, rather than simply showing the WAL insert
pointer which would obviously vary between tests. The tests enclosed
here *also* include the WAL insert pointer so you can manually/visibly
see that the enclosed patch writes no WAL at appropriate times.
psql -f copy_nowal_prep.sql postgres
psql -f copy_nowal_test.sql postgres
Do we want an additional test case along these lines?
Agreed doc changes for Performance Tips forthcoming.
--
Simon Riggs
EnterpriseDB http://www.enterprisedb.com
Index: src/backend/access/heap/heapam.c
===================================================================
RCS file: /projects/cvsroot/pgsql/src/backend/access/heap/heapam.c,v
retrieving revision 1.223
diff -c -r1.223 heapam.c
*** src/backend/access/heap/heapam.c 5 Jan 2007 22:19:22 -0000 1.223
--- src/backend/access/heap/heapam.c 9 Jan 2007 19:41:43 -0000
***************
*** 28,33 ****
--- 28,34 ----
* heap_update - replace a tuple in a relation with another tuple
* heap_markpos - mark scan position
* heap_restrpos - restore position to marked location
+ * heap_sync - sync heap, for when no WAL has been written
*
* NOTES
* This file contains the heap_ routines which implement
***************
*** 50,55 ****
--- 51,57 ----
#include "miscadmin.h"
#include "pgstat.h"
#include "storage/procarray.h"
+ #include "storage/smgr.h"
#include "utils/inval.h"
#include "utils/lsyscache.h"
#include "utils/relcache.h"
***************
*** 1358,1364 ****
* that all new tuples go into new pages not containing any tuples from other
* transactions, that the relation gets fsync'd before commit, and that the
* transaction emits at least one WAL record to ensure RecordTransactionCommit
! * will decide to WAL-log the commit.
*
* use_fsm is passed directly to RelationGetBufferForTuple, which see for
* more info.
--- 1360,1366 ----
* that all new tuples go into new pages not containing any tuples from other
* transactions, that the relation gets fsync'd before commit, and that the
* transaction emits at least one WAL record to ensure RecordTransactionCommit
! * will decide to WAL-log the commit. (see heap_sync() comments also)
*
* use_fsm is passed directly to RelationGetBufferForTuple, which see for
* more info.
***************
*** 1418,1424 ****
*/
if (HeapTupleHasExternal(tup) ||
(MAXALIGN(tup->t_len) > TOAST_TUPLE_THRESHOLD))
! heaptup = toast_insert_or_update(relation, tup, NULL);
else
heaptup = tup;
--- 1420,1426 ----
*/
if (HeapTupleHasExternal(tup) ||
(MAXALIGN(tup->t_len) > TOAST_TUPLE_THRESHOLD))
! heaptup = toast_insert_or_update(relation, tup, NULL, use_wal);
else
heaptup = tup;
***************
*** 1536,1541 ****
--- 1538,1555 ----
}
/*
+ * fast_heap_insert - insert a tuple with options to improve speed
+ *
+ * Currently, this routine allows specifying additional options for speed
+ * in certain cases, such as WAL-avoiding COPY command
+ */
+ Oid
+ fast_heap_insert(Relation relation, HeapTuple tup, bool use_wal)
+ {
+ return heap_insert(relation, tup, GetCurrentCommandId(), use_wal, use_wal);
+ }
+
+ /*
* heap_delete - delete a tuple
*
* NB: do not call this directly unless you are prepared to deal with
***************
*** 2086,2096 ****
*
* Note: below this point, heaptup is the data we actually intend to
* store into the relation; newtup is the caller's original untoasted
! * data.
*/
if (need_toast)
{
! heaptup = toast_insert_or_update(relation, newtup, &oldtup);
newtupsize = MAXALIGN(heaptup->t_len);
}
else
--- 2100,2110 ----
*
* Note: below this point, heaptup is the data we actually intend to
* store into the relation; newtup is the caller's original untoasted
! * data. (We always use WAL for toast table updates.)
*/
if (need_toast)
{
! heaptup = toast_insert_or_update(relation, newtup, &oldtup, true);
newtupsize = MAXALIGN(heaptup->t_len);
}
else
***************
*** 3966,3968 ****
--- 3980,4003 ----
else
appendStringInfo(buf, "UNKNOWN");
}
+
+ /* ----------------
+ * heap_sync - sync a heap, for use when no WAL has been written
+ *
+ * ----------------
+ */
+ void
+ heap_sync(Relation rel)
+ {
+ if (!rel->rd_istemp)
+ {
+ /*
+ * If we skipped using WAL, and it's not a temp relation,
+ * we must force the relation down to disk before it's
+ * safe to commit the transaction. This requires forcing
+ * out any dirty buffers and then doing a forced fsync.
+ */
+ FlushRelationBuffers(rel);
+ smgrimmedsync(rel->rd_smgr);
+ }
+ }
Index: src/backend/access/heap/tuptoaster.c
===================================================================
RCS file: /projects/cvsroot/pgsql/src/backend/access/heap/tuptoaster.c,v
retrieving revision 1.68
diff -c -r1.68 tuptoaster.c
*** src/backend/access/heap/tuptoaster.c 5 Jan 2007 22:19:22 -0000 1.68
--- src/backend/access/heap/tuptoaster.c 9 Jan 2007 19:41:44 -0000
***************
*** 42,48 ****
#undef TOAST_DEBUG
static void toast_delete_datum(Relation rel, Datum value);
! static Datum toast_save_datum(Relation rel, Datum value);
static varattrib *toast_fetch_datum(varattrib *attr);
static varattrib *toast_fetch_datum_slice(varattrib *attr,
int32 sliceoffset, int32 length);
--- 42,48 ----
#undef TOAST_DEBUG
static void toast_delete_datum(Relation rel, Datum value);
! static Datum toast_save_datum(Relation rel, Datum value, bool use_wal);
static varattrib *toast_fetch_datum(varattrib *attr);
static varattrib *toast_fetch_datum_slice(varattrib *attr,
int32 sliceoffset, int32 length);
***************
*** 342,348 ****
* ----------
*/
HeapTuple
! toast_insert_or_update(Relation rel, HeapTuple newtup, HeapTuple oldtup)
{
HeapTuple result_tuple;
TupleDesc tupleDesc;
--- 342,348 ----
* ----------
*/
HeapTuple
! toast_insert_or_update(Relation rel, HeapTuple newtup, HeapTuple oldtup, bool use_wal)
{
HeapTuple result_tuple;
TupleDesc tupleDesc;
***************
*** 612,618 ****
i = biggest_attno;
old_value = toast_values[i];
toast_action[i] = 'p';
! toast_values[i] = toast_save_datum(rel, toast_values[i]);
if (toast_free[i])
pfree(DatumGetPointer(old_value));
--- 612,618 ----
i = biggest_attno;
old_value = toast_values[i];
toast_action[i] = 'p';
! toast_values[i] = toast_save_datum(rel, toast_values[i], use_wal);
if (toast_free[i])
pfree(DatumGetPointer(old_value));
***************
*** 724,730 ****
i = biggest_attno;
old_value = toast_values[i];
toast_action[i] = 'p';
! toast_values[i] = toast_save_datum(rel, toast_values[i]);
if (toast_free[i])
pfree(DatumGetPointer(old_value));
--- 724,730 ----
i = biggest_attno;
old_value = toast_values[i];
toast_action[i] = 'p';
! toast_values[i] = toast_save_datum(rel, toast_values[i], use_wal);
if (toast_free[i])
pfree(DatumGetPointer(old_value));
***************
*** 972,978 ****
* ----------
*/
static Datum
! toast_save_datum(Relation rel, Datum value)
{
Relation toastrel;
Relation toastidx;
--- 972,978 ----
* ----------
*/
static Datum
! toast_save_datum(Relation rel, Datum value, bool use_wal)
{
Relation toastrel;
Relation toastidx;
***************
*** 1057,1063 ****
if (!HeapTupleIsValid(toasttup))
elog(ERROR, "failed to build TOAST tuple");
! simple_heap_insert(toastrel, toasttup);
/*
* Create the index entry. We cheat a little here by not using
--- 1057,1063 ----
if (!HeapTupleIsValid(toasttup))
elog(ERROR, "failed to build TOAST tuple");
! fast_heap_insert(toastrel, toasttup, use_wal);
/*
* Create the index entry. We cheat a little here by not using
Index: src/backend/catalog/index.c
===================================================================
RCS file: /projects/cvsroot/pgsql/src/backend/catalog/index.c,v
retrieving revision 1.276
diff -c -r1.276 index.c
*** src/backend/catalog/index.c 9 Jan 2007 02:14:11 -0000 1.276
--- src/backend/catalog/index.c 9 Jan 2007 19:41:45 -0000
***************
*** 1245,1250 ****
--- 1245,1253 ----
heap_close(pg_class, RowExclusiveLock);
+ /* Remember we did this in current transaction, to allow later optimisations */
+ relation->rd_newRelfilenodeSubid = GetCurrentSubTransactionId();
+
/* Make sure the relfilenode change is visible */
CommandCounterIncrement();
}
Index: src/backend/commands/copy.c
===================================================================
RCS file: /projects/cvsroot/pgsql/src/backend/commands/copy.c,v
retrieving revision 1.274
diff -c -r1.274 copy.c
*** src/backend/commands/copy.c 5 Jan 2007 22:19:25 -0000 1.274
--- src/backend/commands/copy.c 9 Jan 2007 19:41:46 -0000
***************
*** 1652,1657 ****
--- 1652,1658 ----
ExprContext *econtext; /* used for ExecEvalExpr for default atts */
MemoryContext oldcontext = CurrentMemoryContext;
ErrorContextCallback errcontext;
+ bool use_wal = true; /* By default, we use WAL to log db changes */
Assert(cstate->rel);
***************
*** 1843,1848 ****
--- 1844,1871 ----
nfields = file_has_oids ? (attr_count + 1) : attr_count;
field_strings = (char **) palloc(nfields * sizeof(char *));
+ /*
+ * Check for performance optimization by avoiding WAL writes
+ *
+ * If archive logging is not be enabled *and* either
+ * - table is created in same transaction as this COPY
+ * - table data is now being written to new relfilenode
+ * then we can safely avoid writing WAL. Why?
+ * The data files for the table plus toast table/index, plus any indexes
+ * will all be dropped at the end of the transaction if it fails, so we
+ * do not need to worry about inconsistent states.
+ * As mentioned in comments in utils/rel.h, the in-same-transaction test is
+ * not completely reliable, since rd_createSubId can be reset to zero in
+ * certain cases before the end of the creating transaction.
+ * We are doing this for performance only, so we only need to know:
+ * if rd_createSubid != InvalidSubTransactionId then it is *always* just
+ * created. If we have PITR enabled, then we *must* use_wal
+ */
+ if ((cstate->rel->rd_createSubid != InvalidSubTransactionId ||
+ cstate->rel->rd_newRelfilenodeSubid != InvalidSubTransactionId)
+ && !XLogArchivingActive())
+ use_wal = false;
+
/* Initialize state variables */
cstate->fe_eof = false;
cstate->eol_type = EOL_UNKNOWN;
***************
*** 2076,2082 ****
ExecConstraints(resultRelInfo, slot, estate);
/* OK, store the tuple and create index entries for it */
! simple_heap_insert(cstate->rel, tuple);
if (resultRelInfo->ri_NumIndices > 0)
ExecInsertIndexTuples(slot, &(tuple->t_self), estate, false);
--- 2099,2105 ----
ExecConstraints(resultRelInfo, slot, estate);
/* OK, store the tuple and create index entries for it */
! fast_heap_insert(cstate->rel, tuple, use_wal);
if (resultRelInfo->ri_NumIndices > 0)
ExecInsertIndexTuples(slot, &(tuple->t_self), estate, false);
***************
*** 2093,2098 ****
--- 2116,2147 ----
}
}
+ /*
+ * If we skipped writing WAL for heaps, then we need to sync
+ */
+ if (!use_wal)
+ {
+ /* main heap */
+ heap_sync(cstate->rel);
+
+ /* main heap indexes, if any */
+ /* we always use WAL for index inserts, so no need to sync */
+
+ /* toast heap, if any */
+ if (OidIsValid(cstate->rel->rd_rel->reltoastrelid))
+ {
+ Relation toastrel;
+
+ toastrel = heap_open(cstate->rel->rd_rel->reltoastrelid,
+ AccessShareLock);
+ heap_sync(toastrel);
+ heap_close(toastrel, AccessShareLock);
+ }
+
+ /* toast index, if toast heap */
+ /* we always use WAL for index inserts, so no need to sync */
+ }
+
/* Done, clean up */
error_context_stack = errcontext.previous;
Index: src/backend/executor/execMain.c
===================================================================
RCS file: /projects/cvsroot/pgsql/src/backend/executor/execMain.c,v
retrieving revision 1.283
diff -c -r1.283 execMain.c
*** src/backend/executor/execMain.c 5 Jan 2007 22:19:27 -0000 1.283
--- src/backend/executor/execMain.c 9 Jan 2007 19:41:47 -0000
***************
*** 2516,2526 ****
*/
if (!estate->es_into_relation_use_wal &&
!estate->es_into_relation_descriptor->rd_istemp)
! {
! FlushRelationBuffers(estate->es_into_relation_descriptor);
! /* FlushRelationBuffers will have opened rd_smgr */
! smgrimmedsync(estate->es_into_relation_descriptor->rd_smgr);
! }
/* close rel, but keep lock until commit */
heap_close(estate->es_into_relation_descriptor, NoLock);
--- 2516,2522 ----
*/
if (!estate->es_into_relation_use_wal &&
!estate->es_into_relation_descriptor->rd_istemp)
! heap_sync(estate->es_into_relation_descriptor);
/* close rel, but keep lock until commit */
heap_close(estate->es_into_relation_descriptor, NoLock);
Index: src/backend/utils/cache/relcache.c
===================================================================
RCS file: /projects/cvsroot/pgsql/src/backend/utils/cache/relcache.c,v
retrieving revision 1.254
diff -c -r1.254 relcache.c
*** src/backend/utils/cache/relcache.c 9 Jan 2007 02:14:15 -0000 1.254
--- src/backend/utils/cache/relcache.c 9 Jan 2007 19:41:49 -0000
***************
*** 836,841 ****
--- 836,842 ----
relation->rd_refcnt = 0;
relation->rd_isnailed = false;
relation->rd_createSubid = InvalidSubTransactionId;
+ relation->rd_newRelfilenodeSubid = InvalidSubTransactionId;
relation->rd_istemp = isTempNamespace(relation->rd_rel->relnamespace);
/*
***************
*** 1358,1363 ****
--- 1359,1365 ----
*/
relation->rd_isnailed = true;
relation->rd_createSubid = InvalidSubTransactionId;
+ relation->rd_newRelfilenodeSubid = InvalidSubTransactionId;
relation->rd_istemp = false;
/*
***************
*** 1769,1774 ****
--- 1771,1777 ----
Oid save_relid = RelationGetRelid(relation);
int old_refcnt = relation->rd_refcnt;
SubTransactionId old_createSubid = relation->rd_createSubid;
+ SubTransactionId old_newRelfilenodeSubid = relation->rd_newRelfilenodeSubid;
TupleDesc old_att = relation->rd_att;
RuleLock *old_rules = relation->rd_rules;
MemoryContext old_rulescxt = relation->rd_rulescxt;
***************
*** 1787,1792 ****
--- 1790,1797 ----
}
relation->rd_refcnt = old_refcnt;
relation->rd_createSubid = old_createSubid;
+ relation->rd_newRelfilenodeSubid = old_newRelfilenodeSubid;
+
if (equalTupleDescs(old_att, relation->rd_att))
{
/* needn't flush typcache here */
***************
*** 1827,1833 ****
{
bool rebuild;
! if (relation->rd_createSubid != InvalidSubTransactionId)
{
/*
* New relcache entries are always rebuilt, not flushed; else we'd
--- 1832,1839 ----
{
bool rebuild;
! if (relation->rd_createSubid != InvalidSubTransactionId ||
! relation->rd_newRelfilenodeSubid != InvalidSubTransactionId)
{
/*
* New relcache entries are always rebuilt, not flushed; else we'd
***************
*** 1909,1914 ****
--- 1915,1923 ----
* so we do not touch new-in-transaction relations; they cannot be targets
* of cross-backend SI updates (and our own updates now go through a
* separate linked list that isn't limited by the SI message buffer size).
+ * We don't do anything special for newRelfilenode-in-transaction relations,
+ * though since we have a lock on the relation nobody else should be
+ * generating cache invalidation messages for it anyhow.
*
* We do this in two phases: the first pass deletes deletable items, and
* the second one rebuilds the rebuildable items. This is essential for
***************
*** 2085,2090 ****
--- 2094,2100 ----
continue;
}
}
+ relation->rd_newRelfilenodeSubid = InvalidSubTransactionId;
/*
* Flush any temporary index list.
***************
*** 2146,2151 ****
--- 2156,2168 ----
continue;
}
}
+ if (relation->rd_newRelfilenodeSubid == mySubid)
+ {
+ if (isCommit)
+ relation->rd_newRelfilenodeSubid = parentSubid;
+ else
+ relation->rd_newRelfilenodeSubid = InvalidSubTransactionId;
+ }
/*
* Flush any temporary index list.
***************
*** 2235,2240 ****
--- 2252,2258 ----
/* it's being created in this transaction */
rel->rd_createSubid = GetCurrentSubTransactionId();
+ rel->rd_newRelfilenodeSubid = InvalidSubTransactionId;
/* must flag that we have rels created in this transaction */
need_eoxact_work = true;
***************
*** 3392,3397 ****
--- 3410,3416 ----
rel->rd_indexlist = NIL;
rel->rd_oidindex = InvalidOid;
rel->rd_createSubid = InvalidSubTransactionId;
+ rel->rd_newRelfilenodeSubid = InvalidSubTransactionId;
rel->rd_amcache = NULL;
MemSet(&rel->pgstat_info, 0, sizeof(rel->pgstat_info));
Index: src/include/access/heapam.h
===================================================================
RCS file: /projects/cvsroot/pgsql/src/include/access/heapam.h,v
retrieving revision 1.118
diff -c -r1.118 heapam.h
*** src/include/access/heapam.h 5 Jan 2007 22:19:51 -0000 1.118
--- src/include/access/heapam.h 9 Jan 2007 19:41:49 -0000
***************
*** 178,183 ****
--- 178,186 ----
extern void simple_heap_update(Relation relation, ItemPointer otid,
HeapTuple tup);
+ extern Oid fast_heap_insert(Relation relation, HeapTuple tup, bool use_wal);
+
+
extern void heap_markpos(HeapScanDesc scan);
extern void heap_restrpos(HeapScanDesc scan);
***************
*** 236,239 ****
--- 239,244 ----
extern HeapTuple heap_addheader(int natts, bool withoid,
Size structlen, void *structure);
+ extern void heap_sync(Relation relation);
+
#endif /* HEAPAM_H */
Index: src/include/access/tuptoaster.h
===================================================================
RCS file: /projects/cvsroot/pgsql/src/include/access/tuptoaster.h,v
retrieving revision 1.29
diff -c -r1.29 tuptoaster.h
*** src/include/access/tuptoaster.h 5 Jan 2007 22:19:51 -0000 1.29
--- src/include/access/tuptoaster.h 9 Jan 2007 19:41:49 -0000
***************
*** 69,75 ****
* ----------
*/
extern HeapTuple toast_insert_or_update(Relation rel,
! HeapTuple newtup, HeapTuple oldtup);
/* ----------
* toast_delete -
--- 69,75 ----
* ----------
*/
extern HeapTuple toast_insert_or_update(Relation rel,
! HeapTuple newtup, HeapTuple oldtup, bool use_wal);
/* ----------
* toast_delete -
Index: src/include/utils/rel.h
===================================================================
RCS file: /projects/cvsroot/pgsql/src/include/utils/rel.h,v
retrieving revision 1.95
diff -c -r1.95 rel.h
*** src/include/utils/rel.h 9 Jan 2007 02:14:16 -0000 1.95
--- src/include/utils/rel.h 9 Jan 2007 19:41:49 -0000
***************
*** 137,142 ****
--- 137,143 ----
char rd_indexvalid; /* state of rd_indexlist: 0 = not valid, 1 =
* valid, 2 = temporarily forced */
SubTransactionId rd_createSubid; /* rel was created in current xact */
+ SubTransactionId rd_newRelfilenodeSubid; /* rel had new relfilenode in current xact */
/*
* rd_createSubid is the ID of the highest subtransaction the rel has
drop table if exists fastcopy1;
create table fastcopy1 as select generate_series(1,100000)::integer, repeat('a', 1500)::text;
copy fastcopy1
to '/tmp/fastcopy1' binary;
drop table fastcopy1;
drop table if exists fastcopy2;
create table fastcopy2 as select generate_series(1,100000)::integer;
copy fastcopy2
to '/tmp/fastcopy2' binary;
drop table fastcopy2;
-- table to test whether particular commands write WAL or not
-- relies on the fact that temp table writes do not write WAL
drop table if exists xlogpos;
create temp table xlogpos (id integer primary key, pos text);
insert into xlogpos values (1, pg_current_xlog_insert_location());
create or replace function wasWALwritten (expectation boolean) returns text
as $$
declare
WALresult boolean;
begin
select (case when position(pg_current_xlog_insert_location() in pos) = 1
then false
else true
end) into WALresult
from xlogpos where id = 1;
if (WALresult and expectation) or (not WALresult and not expectation) then
return true;
else
return false;
end if;
end;
$$ language plpgsql;
update xlogpos set pos = pg_current_xlog_insert_location() where id = 1;
--returns false because our expectation that no WAL has been written should be true
select wasWALwritten(true);
update xlogpos set pos = pg_current_xlog_insert_location() where id = 1;
--returns true because our expectation that no WAL has been written should be true
select wasWALwritten(false);
drop table if exists xlogpos;
create temp table xlogpos (id integer primary key, pos text);
insert into xlogpos values (1, pg_current_xlog_insert_location());
drop table if exists fastcopy1;
create table fastcopy1
(col1 integer
,col2 text);
checkpoint;
select pg_current_xlog_insert_location();
update xlogpos set pos = pg_current_xlog_insert_location() where id = 1;
\echo slow COPY
copy fastcopy1
from '/tmp/fastcopy1' binary;
select wasWALwritten(true);
select pg_current_xlog_insert_location();
\echo slow vacuum
vacuum fastcopy1;
drop table if exists fastcopy1;
checkpoint;
begin;
create table fastcopy1
(col1 integer
,col2 text);
select pg_current_xlog_insert_location();
update xlogpos set pos = pg_current_xlog_insert_location() where id = 1;
\echo fast COPY
copy fastcopy1
from '/tmp/fastcopy1' binary;
select wasWALwritten(false) as waswalavoided;
select pg_current_xlog_insert_location();
commit;
checkpoint;
begin;
truncate fastcopy1;
select pg_current_xlog_insert_location();
update xlogpos set pos = pg_current_xlog_insert_location() where id = 1;
\echo fast COPY
copy fastcopy1
from '/tmp/fastcopy1' binary;
select wasWALwritten(false) as waswalavoided;
select pg_current_xlog_insert_location();
commit;
select count(*) from fastcopy1;
checkpoint;
begin;
truncate fastcopy1;
savepoint sp;
select pg_current_xlog_insert_location();
update xlogpos set pos = pg_current_xlog_insert_location() where id = 1;
\echo fast COPY
copy fastcopy1
from '/tmp/fastcopy1' binary;
select wasWALwritten(false) as waswalavoided;
select pg_current_xlog_insert_location();
rollback to sp;
commit;
select count(*) from fastcopy1;
drop table if exists fastcopy2;
create table fastcopy2
(col1 integer);
checkpoint;
select pg_current_xlog_insert_location();
update xlogpos set pos = pg_current_xlog_insert_location() where id = 1;
\echo slow COPY
copy fastcopy2
from '/tmp/fastcopy2' binary;
select wasWALwritten(true);
select pg_current_xlog_insert_location();
\echo slow vacuum
vacuum fastcopy2;
drop table if exists fastcopy2;
checkpoint;
begin;
create table fastcopy2
(col1 integer);
select pg_current_xlog_insert_location();
update xlogpos set pos = pg_current_xlog_insert_location() where id = 1;
\echo fast COPY
copy fastcopy2
from '/tmp/fastcopy2' binary;
select wasWALwritten(false) as waswalavoided;
select pg_current_xlog_insert_location();
commit;
checkpoint;
begin;
truncate fastcopy2;
select pg_current_xlog_insert_location();
update xlogpos set pos = pg_current_xlog_insert_location() where id = 1;
\echo fast COPY
copy fastcopy2
from '/tmp/fastcopy2' binary;
select wasWALwritten(false) as waswalavoided;
select pg_current_xlog_insert_location();
commit;
select count(*) from fastcopy2;
checkpoint;
begin;
truncate fastcopy2;
savepoint sp;
select pg_current_xlog_insert_location();
update xlogpos set pos = pg_current_xlog_insert_location() where id = 1;
\echo fast COPY
copy fastcopy2
from '/tmp/fastcopy2' binary;
select wasWALwritten(false) as waswalavoided;
select pg_current_xlog_insert_location();
rollback to sp;
commit;
select count(*) from fastcopy2;
---------------------------(end of broadcast)---------------------------
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