Re: [PATCH 11/14] Introduce wal decoding via catalog timetravel

On 12-11-14 08:17 PM, Andres Freund wrote:

I am getting errors like the following when I try to use either your
test_decoding plugin or my own (which does even less than yours)

LOG: database system is ready to accept connections
LOG: autovacuum launcher started
WARNING: connecting to
WARNING: Initiating logical rep
LOG: computed new xmin: 773
LOG: start reading from 0/17F5D58, scrolled back to 0/17F4000
LOG: got new xmin 773 at 25124280
LOG: found initial snapshot (via running xacts). Done: 1
WARNING: reached consistent point, stopping!
WARNING: Starting logical replication
LOG: start reading from 0/17F5D58, scrolled back to 0/17F4000
LOG: found initial snapshot (via running xacts). Done: 1
FATAL: cannot read pg_class without having selected a database
TRAP: FailedAssertion("!(SHMQueueEmpty(&(MyProc->myProcLocks[i])))",
File: "proc.c", Line: 759)

This seems to be happening under the calls at
reorderbuffer.c:832 if (!SnapBuildHasCatalogChanges(NULL, xid,
&change->relnode))

The sequence of events I do is:
1. start pg_receivellog
2. run a checkpoint
3. Attach to the walsender process with gdb
4. Start a new client connection with psql and do 'INSERT INTO a values
(1)' twice.

(skipping step 3 doesn't make a difference)

I

> This introduces several things:
> * 'reorderbuffer' module which reassembles transactions from a stream of interspersed changes
> * 'snapbuilder' which builds catalog snapshots so that tuples from wal can be understood
> * logging more data into wal to facilitate logical decoding
> * wal decoding into an reorderbuffer
> * shared library output plugins with 5 callbacks
> * init
> * begin
> * change
> * commit
> * walsender infrastructur to stream out changes and to keep the global xmin low enough
> * INIT_LOGICAL_REPLICATION $plugin; waits till a consistent snapshot is built and returns
> * initial LSN
> * replication slot identifier
> * id of a pg_export() style snapshot
> * START_LOGICAL_REPLICATION $id $lsn; streams out changes
> * uses named output plugins for output specification
>
> Todo:
> * testing infrastructure (isolationtester)
> * persistence/spilling to disk of built snapshots, longrunning
> transactions
> * user docs
> * more frequent lowering of xmins
> * more docs about the internals
> * support for user declared catalog tables
> * actual exporting of initial pg_export snapshots after
> INIT_LOGICAL_REPLICATION
> * own shared memory segment instead of piggybacking on walsender's
> * nicer interface between snapbuild.c, reorderbuffer.c, decode.c and the
> outside.
> * more frequent xl_running_xid's so xmin can be upped more frequently
> * add STOP_LOGICAL_REPLICATION $id
> ---
> src/backend/access/heap/heapam.c | 280 +++++-
> src/backend/access/transam/xlog.c | 1 +
> src/backend/catalog/index.c | 74 ++
> src/backend/replication/Makefile | 2 +
> src/backend/replication/logical/Makefile | 19 +
> src/backend/replication/logical/decode.c | 496 ++++++++++
> src/backend/replication/logical/logicalfuncs.c | 247 +++++
> src/backend/replication/logical/reorderbuffer.c | 1156 +++++++++++++++++++++++
> src/backend/replication/logical/snapbuild.c | 1144 ++++++++++++++++++++++
> src/backend/replication/repl_gram.y | 32 +-
> src/backend/replication/repl_scanner.l | 2 +
> src/backend/replication/walsender.c | 566 ++++++++++-
> src/backend/storage/ipc/procarray.c | 23 +
> src/backend/storage/ipc/standby.c | 8 +-
> src/backend/utils/cache/inval.c | 2 +-
> src/backend/utils/cache/relcache.c | 3 +-
> src/backend/utils/misc/guc.c | 11 +
> src/backend/utils/time/tqual.c | 249 +++++
> src/bin/pg_controldata/pg_controldata.c | 2 +
> src/include/access/heapam_xlog.h | 23 +
> src/include/access/transam.h | 5 +
> src/include/access/xlog.h | 3 +-
> src/include/catalog/index.h | 4 +
> src/include/nodes/nodes.h | 2 +
> src/include/nodes/replnodes.h | 22 +
> src/include/replication/decode.h | 21 +
> src/include/replication/logicalfuncs.h | 44 +
> src/include/replication/output_plugin.h | 76 ++
> src/include/replication/reorderbuffer.h | 284 ++++++
> src/include/replication/snapbuild.h | 128 +++
> src/include/replication/walsender.h | 1 +
> src/include/replication/walsender_private.h | 34 +-
> src/include/storage/itemptr.h | 3 +
> src/include/storage/sinval.h | 2 +
> src/include/utils/tqual.h | 31 +-
> 35 files changed, 4966 insertions(+), 34 deletions(-)
> create mode 100644 src/backend/replication/logical/Makefile
> create mode 100644 src/backend/replication/logical/decode.c
> create mode 100644 src/backend/replication/logical/logicalfuncs.c
> create mode 100644 src/backend/replication/logical/reorderbuffer.c
> create mode 100644 src/backend/replication/logical/snapbuild.c
> create mode 100644 src/include/replication/decode.h
> create mode 100644 src/include/replication/logicalfuncs.h
> create mode 100644 src/include/replication/output_plugin.h
> create mode 100644 src/include/replication/reorderbuffer.h
> create mode 100644 src/include/replication/snapbuild.h
>
>
>