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When implementing a replication solution ontop of logical decoding, two
related problems exist:
* How to safely keep track of replication progress
* How to change replication behavior, based on the origin of a row;
e.g. to avoid loops in bi-directional replication setups
The solution to these problems, as implemented here, consist out of
three parts:
1) 'replication origins', which identify nodes in a replication setup.
2) 'replication progress tracking', which remembers, for each
replication origin, how far replay has progressed in a efficient and
crash safe manner.
3) The ability to filter out changes performed on the behest of a
replication origin during logical decoding; this allows complex
replication topologies. E.g. by filtering all replayed changes out.
Most of this could also be implemented in "userspace", e.g. by inserting
additional rows contain origin information, but that ends up being much
less efficient and more complicated. We don't want to require various
replication solutions to reimplement logic for this independently. The
infrastructure is intended to be generic enough to be reusable.
This infrastructure also replaces the 'nodeid' infrastructure of commit
timestamps. It is intended to provide all the former capabilities,
except that there's only 2^16 different origins; but now they integrate
with logical decoding. Additionally more functionality is accessible via
SQL. Since the commit timestamp infrastructure has also been introduced
in 9.5 (commit 73c986add) changing the API is not a problem.
For now the number of origins for which the replication progress can be
tracked simultaneously is determined by the max_replication_slots
GUC. That GUC is not a perfect match to configure this, but there
doesn't seem to be sufficient reason to introduce a separate new one.
Bumps both catversion and wal page magic.
Author: Andres Freund, with contributions from Petr Jelinek and Craig Ringer
Reviewed-By: Heikki Linnakangas, Petr Jelinek, Robert Haas, Steve Singer
Discussion: 20150216002155.GI15326@awork2.anarazel.de,
20140923182422.GA15776@alap3.anarazel.de,
20131114172632.GE7522@alap2.anarazel.de
102 lines
2.8 KiB
C
102 lines
2.8 KiB
C
/*-------------------------------------------------------------------------
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* logical.h
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* PostgreSQL logical decoding coordination
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*
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* Copyright (c) 2012-2015, PostgreSQL Global Development Group
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*
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*-------------------------------------------------------------------------
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*/
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#ifndef LOGICAL_H
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#define LOGICAL_H
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#include "replication/slot.h"
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#include "access/xlog.h"
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#include "access/xlogreader.h"
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#include "replication/output_plugin.h"
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struct LogicalDecodingContext;
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typedef void (*LogicalOutputPluginWriterWrite) (
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struct LogicalDecodingContext *lr,
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XLogRecPtr Ptr,
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TransactionId xid,
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bool last_write
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);
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typedef LogicalOutputPluginWriterWrite LogicalOutputPluginWriterPrepareWrite;
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typedef struct LogicalDecodingContext
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{
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/* memory context this is all allocated in */
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MemoryContext context;
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/* infrastructure pieces */
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XLogReaderState *reader;
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ReplicationSlot *slot;
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struct ReorderBuffer *reorder;
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struct SnapBuild *snapshot_builder;
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OutputPluginCallbacks callbacks;
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OutputPluginOptions options;
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/*
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* User specified options
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*/
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List *output_plugin_options;
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/*
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* User-Provided callback for writing/streaming out data.
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*/
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LogicalOutputPluginWriterPrepareWrite prepare_write;
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LogicalOutputPluginWriterWrite write;
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/*
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* Output buffer.
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*/
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StringInfo out;
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/*
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* Private data pointer of the output plugin.
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*/
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void *output_plugin_private;
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/*
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* Private data pointer for the data writer.
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*/
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void *output_writer_private;
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/*
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* State for writing output.
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*/
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bool accept_writes;
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bool prepared_write;
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XLogRecPtr write_location;
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TransactionId write_xid;
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} LogicalDecodingContext;
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extern void CheckLogicalDecodingRequirements(void);
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extern LogicalDecodingContext *CreateInitDecodingContext(char *plugin,
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List *output_plugin_options,
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XLogPageReadCB read_page,
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LogicalOutputPluginWriterPrepareWrite prepare_write,
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LogicalOutputPluginWriterWrite do_write);
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extern LogicalDecodingContext *CreateDecodingContext(
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XLogRecPtr start_lsn,
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List *output_plugin_options,
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XLogPageReadCB read_page,
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LogicalOutputPluginWriterPrepareWrite prepare_write,
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LogicalOutputPluginWriterWrite do_write);
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extern void DecodingContextFindStartpoint(LogicalDecodingContext *ctx);
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extern bool DecodingContextReady(LogicalDecodingContext *ctx);
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extern void FreeDecodingContext(LogicalDecodingContext *ctx);
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extern void LogicalIncreaseXminForSlot(XLogRecPtr lsn, TransactionId xmin);
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extern void LogicalIncreaseRestartDecodingForSlot(XLogRecPtr current_lsn,
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XLogRecPtr restart_lsn);
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extern void LogicalConfirmReceivedLocation(XLogRecPtr lsn);
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extern bool filter_by_origin_cb_wrapper(LogicalDecodingContext *ctx, RepOriginId origin_id);
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#endif
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