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Introduce logical decoding.

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This feature, building on previous commits, allows the write-ahead log
stream to be decoded into a series of logical changes; that is,
inserts, updates, and deletes and the transactions which contain them.
It is capable of handling decoding even across changes to the schema
of the effected tables.  The output format is controlled by a
so-called "output plugin"; an example is included.  To make use of
this in a real replication system, the output plugin will need to be
modified to produce output in the format appropriate to that system,
and to perform filtering.

Currently, information can be extracted from the logical decoding
system only via SQL; future commits will add the ability to stream
changes via walsender.

Andres Freund, with review and other contributions from many other
people, including Álvaro Herrera, Abhijit Menon-Sen, Peter Gheogegan,
Kevin Grittner, Robert Haas, Heikki Linnakangas, Fujii Masao, Abhijit
Menon-Sen, Michael Paquier, Simon Riggs, Craig Ringer, and Steve
Singer.
This commit is contained in:
Robert Haas
2014-03-03 16:32:18 -05:00
parent de94b47c0a
commit b89e151054
89 changed files with 12998 additions and 194 deletions
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57
src/backend/utils/cache/relcache.c vendored
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@ -73,6 +73,7 @@
#include "utils/memutils.h"
#include "utils/relmapper.h"
#include "utils/resowner_private.h"
#include "utils/snapmgr.h"
#include "utils/syscache.h"
#include "utils/tqual.h"
@ -235,7 +236,7 @@ static void formrdesc(const char *relationName, Oid relationReltype,
bool isshared, bool hasoids,
int natts, const FormData_pg_attribute *attrs);
static HeapTuple ScanPgRelation(Oid targetRelId, bool indexOK);
static HeapTuple ScanPgRelation(Oid targetRelId, bool indexOK, bool force_non_historic);
static Relation AllocateRelationDesc(Form_pg_class relp);
static void RelationParseRelOptions(Relation relation, HeapTuple tuple);
static void RelationBuildTupleDesc(Relation relation);
@ -274,12 +275,13 @@ static void unlink_initfile(const char *initfilename);
* and must eventually be freed with heap_freetuple.
*/
static HeapTuple
ScanPgRelation(Oid targetRelId, bool indexOK)
ScanPgRelation(Oid targetRelId, bool indexOK, bool force_non_historic)
{
HeapTuple pg_class_tuple;
Relation pg_class_desc;
SysScanDesc pg_class_scan;
ScanKeyData key[1];
Snapshot snapshot;
/*
* If something goes wrong during backend startup, we might find ourselves
@ -305,9 +307,20 @@ ScanPgRelation(Oid targetRelId, bool indexOK)
* scan by setting indexOK == false.
*/
pg_class_desc = heap_open(RelationRelationId, AccessShareLock);
/*
* The caller might need a tuple that's newer than the one the historic
* snapshot; currently the only case requiring to do so is looking up the
* relfilenode of non mapped system relations during decoding.
*/
if (force_non_historic)
snapshot = GetNonHistoricCatalogSnapshot(RelationRelationId);
else
snapshot = GetCatalogSnapshot(RelationRelationId);
pg_class_scan = systable_beginscan(pg_class_desc, ClassOidIndexId,
indexOK && criticalRelcachesBuilt,
NULL,
snapshot,
1, key);
pg_class_tuple = systable_getnext(pg_class_scan);
@ -836,7 +849,7 @@ RelationBuildDesc(Oid targetRelId, bool insertIt)
/*
* find the tuple in pg_class corresponding to the given relation id
*/
pg_class_tuple = ScanPgRelation(targetRelId, true);
pg_class_tuple = ScanPgRelation(targetRelId, true, false);
/*
* if no such tuple exists, return NULL
@ -989,8 +1002,42 @@ RelationInitPhysicalAddr(Relation relation)
relation->rd_node.dbNode = InvalidOid;
else
relation->rd_node.dbNode = MyDatabaseId;
if (relation->rd_rel->relfilenode)
{
/*
* Even if we are using a decoding snapshot that doesn't represent
* the current state of the catalog we need to make sure the
* filenode points to the current file since the older file will
* be gone (or truncated). The new file will still contain older
* rows so lookups in them will work correctly. This wouldn't work
* correctly if rewrites were allowed to change the schema in a
* noncompatible way, but those are prevented both on catalog
* tables and on user tables declared as additional catalog
* tables.
*/
if (HistoricSnapshotActive()
&& RelationIsAccessibleInLogicalDecoding(relation)
&& IsTransactionState())
{
HeapTuple phys_tuple;
Form_pg_class physrel;
phys_tuple = ScanPgRelation(RelationGetRelid(relation),
RelationGetRelid(relation) != ClassOidIndexId,
true);
if (!HeapTupleIsValid(phys_tuple))
elog(ERROR, "could not find pg_class entry for %u",
RelationGetRelid(relation));
physrel = (Form_pg_class) GETSTRUCT(phys_tuple);
relation->rd_rel->reltablespace = physrel->reltablespace;
relation->rd_rel->relfilenode = physrel->relfilenode;
heap_freetuple(phys_tuple);
}
relation->rd_node.relNode = relation->rd_rel->relfilenode;
}
else
{
/* Consult the relation mapper */
@ -1742,7 +1789,7 @@ RelationReloadIndexInfo(Relation relation)
* for pg_class_oid_index ...
*/
indexOK = (RelationGetRelid(relation) != ClassOidIndexId);
pg_class_tuple = ScanPgRelation(RelationGetRelid(relation), indexOK);
pg_class_tuple = ScanPgRelation(RelationGetRelid(relation), indexOK, false);
if (!HeapTupleIsValid(pg_class_tuple))
elog(ERROR, "could not find pg_class tuple for index %u",
RelationGetRelid(relation));