Deduplicate freeze plans in freeze WAL records.

Make heapam WAL records that describe freezing performed by VACUUM more
space efficient by storing each distinct "freeze plan" once, alongside
an array of associated page offset numbers (one per freeze plan).  The
freeze plans required for most heap pages tend to naturally have a great
deal of redundancy, so this technique is very effective in practice.  It
often leads to freeze WAL records that are less than 20% of the size of
equivalent WAL records generated using the previous approach.

The freeze plan concept was introduced by commit 3b97e6823b, which fixed
bugs in VACUUM's handling of MultiXacts.  We retain the concept of
freeze plans, but go back to using page offset number arrays.  There is
no loss of generality here because deduplication is an additive process
that gets applied mechanically when FREEZE_PAGE WAL records are built.

More than anything else, freeze plan deduplication is an optimization
that reduces the marginal cost of freezing additional tuples on pages
that will need to have at least one or two tuples frozen in any case.
Ongoing work that adds page-level freezing to VACUUM will take full
advantage of the improved cost profile through batching.

Also refactor some of the details surrounding recovery conflicts needed
to REDO freeze records in passing: make original execution responsible
for generating a standard latestRemovedXid cutoff, rather than working
backwards to get the same cutoff in the REDO routine.  Bugfix commit
66fbcb0d2e did it the other way around, which is equivalent but obscures
what's going on.

Also rename the cutoff field from the WAL record/struct (rename the
field cutoff_xid to latestRemovedXid to match similar WAL records).
Processing of conflicts by REDO routines is already completely uniform,
so tools like pg_waldump should present the information driving the
process uniformly.  There are two remaining WAL record types that still
don't quite follow this convention (heapam's VISIBLE record type and
SP-GiST's VACUUM_REDIRECT record type).  They can be brought into line
by later work that totally standardizes how the cutoffs are presented.

Bump XLOG_PAGE_MAGIC.

Author: Peter Geoghegan <[email protected]>
Reviewed-By: Masahiko Sawada <[email protected]>
Reviewed-By: Nathan Bossart <[email protected]>
Reviewed-By: Justin Pryzby <[email protected]>
Discussion: https://postgr.es/m/CAH2-Wz=XytErMnb8FAyFd+OQEbiipB0Q2FmFdXrggPL4VBnRYQ@mail.gmail.com

1 files changed, 22 insertions, 0 deletions

diff --git a/src/include/access/heapam.h b/src/include/access/heapam.h
index 5b078757404..ebe723abb06 100644
--- a/src/include/access/heapam.h
+++ b/src/include/access/heapam.h
@@ -99,6 +99,19 @@ typedef enum
 	HEAPTUPLE_DELETE_IN_PROGRESS	/* deleting xact is still in progress */
 } HTSV_Result;
 
+/* heap_prepare_freeze_tuple state describing how to freeze a tuple */
+typedef struct HeapTupleFreeze
+{
+	/* Fields describing how to process tuple */
+	TransactionId xmax;
+	uint16		t_infomask2;
+	uint16		t_infomask;
+	uint8		frzflags;
+
+	/* Page offset number for tuple */
+	OffsetNumber offset;
+} HeapTupleFreeze;
+
 /* ----------------
  *		function prototypes for heap access method
  *
@@ -164,6 +177,15 @@ extern TM_Result heap_lock_tuple(Relation relation, HeapTuple tuple,
 								 Buffer *buffer, struct TM_FailureData *tmfd);
 
 extern void heap_inplace_update(Relation relation, HeapTuple tuple);
+extern bool heap_prepare_freeze_tuple(HeapTupleHeader tuple,
+									  TransactionId relfrozenxid, TransactionId relminmxid,
+									  TransactionId cutoff_xid, TransactionId cutoff_multi,
+									  HeapTupleFreeze *frz, bool *totally_frozen,
+									  TransactionId *relfrozenxid_out,
+									  MultiXactId *relminmxid_out);
+extern void heap_freeze_execute_prepared(Relation rel, Buffer buffer,
+										 TransactionId FreezeLimit,
+										 HeapTupleFreeze *tuples, int ntuples);
 extern bool heap_freeze_tuple(HeapTupleHeader tuple,
 							  TransactionId relfrozenxid, TransactionId relminmxid,
 							  TransactionId cutoff_xid, TransactionId cutoff_multi);