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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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15
src/backend/commands/dbcommands.c
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@ -45,6 +45,7 @@
#include "miscadmin.h"
#include "pgstat.h"
#include "postmaster/bgwriter.h"
#include "replication/slot.h"
#include "storage/copydir.h"
#include "storage/fd.h"
#include "storage/lmgr.h"
@ -750,6 +751,7 @@ dropdb(const char *dbname, bool missing_ok)
HeapTuple tup;
int notherbackends;
int npreparedxacts;
int nslots, nslots_active;
/*
* Look up the target database's OID, and get exclusive lock on it. We
@ -806,6 +808,19 @@ dropdb(const char *dbname, bool missing_ok)
(errcode(ERRCODE_OBJECT_IN_USE),
errmsg("cannot drop the currently open database")));
/*
* Check whether there are, possibly unconnected, logical slots that refer
* to the to-be-dropped database. The database lock we are holding
* prevents the creation of new slots using the database.
*/
if (ReplicationSlotsCountDBSlots(db_id, &nslots, &nslots_active))
ereport(ERROR,
(errcode(ERRCODE_OBJECT_IN_USE),
errmsg("database \"%s\" is used by a logical decoding slot",
dbname),
errdetail("There are %d slot(s), %d of them active",
nslots, nslots_active)));
/*
* Check for other backends in the target database. (Because we hold the
* database lock, no new ones can start after this.)