200 lines
6.2 KiB
C
200 lines
6.2 KiB
C
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/*-------------------------------------------------------------------------
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*
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* snapbuild_internal.h
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* This file contains declarations for logical decoding utility
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* functions for internal use.
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*
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* Copyright (c) 2024-2025, PostgreSQL Global Development Group
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*
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* src/include/replication/snapbuild_internal.h
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*
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*-------------------------------------------------------------------------
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*/
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#ifndef SNAPBUILD_INTERNAL_H
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#define SNAPBUILD_INTERNAL_H
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#include "port/pg_crc32c.h"
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#include "replication/reorderbuffer.h"
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#include "replication/snapbuild.h"
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/*
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* This struct contains the current state of the snapshot building
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* machinery. It is exposed to the public, so pay attention when changing its
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* contents.
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*/
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struct SnapBuild
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{
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/* how far are we along building our first full snapshot */
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SnapBuildState state;
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/* private memory context used to allocate memory for this module. */
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MemoryContext context;
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/* all transactions < than this have committed/aborted */
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TransactionId xmin;
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/* all transactions >= than this are uncommitted */
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TransactionId xmax;
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/*
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* Don't replay commits from an LSN < this LSN. This can be set externally
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* but it will also be advanced (never retreat) from within snapbuild.c.
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*/
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XLogRecPtr start_decoding_at;
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/*
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* LSN at which two-phase decoding was enabled or LSN at which we found a
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* consistent point at the time of slot creation.
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*
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* The prepared transactions, that were skipped because previously
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* two-phase was not enabled or are not covered by initial snapshot, need
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* to be sent later along with commit prepared and they must be before
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* this point.
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*/
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XLogRecPtr two_phase_at;
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/*
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* Don't start decoding WAL until the "xl_running_xacts" information
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* indicates there are no running xids with an xid smaller than this.
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*/
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TransactionId initial_xmin_horizon;
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/* Indicates if we are building full snapshot or just catalog one. */
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bool building_full_snapshot;
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/*
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* Indicates if we are using the snapshot builder for the creation of a
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* logical replication slot. If it's true, the start point for decoding
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* changes is not determined yet. So we skip snapshot restores to properly
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* find the start point. See SnapBuildFindSnapshot() for details.
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*/
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bool in_slot_creation;
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/*
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* Snapshot that's valid to see the catalog state seen at this moment.
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*/
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Snapshot snapshot;
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/*
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* LSN of the last location we are sure a snapshot has been serialized to.
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*/
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XLogRecPtr last_serialized_snapshot;
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/*
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* The reorderbuffer we need to update with usable snapshots et al.
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*/
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ReorderBuffer *reorder;
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/*
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* TransactionId at which the next phase of initial snapshot building will
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* happen. InvalidTransactionId if not known (i.e. SNAPBUILD_START), or
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* when no next phase necessary (SNAPBUILD_CONSISTENT).
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*/
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TransactionId next_phase_at;
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/*
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* Array of transactions which could have catalog changes that committed
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* between xmin and xmax.
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*/
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struct
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{
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/* number of committed transactions */
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size_t xcnt;
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/* available space for committed transactions */
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size_t xcnt_space;
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/*
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* Until we reach a CONSISTENT state, we record commits of all
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* transactions, not just the catalog changing ones. Record when that
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* changes so we know we cannot export a snapshot safely anymore.
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*/
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bool includes_all_transactions;
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/*
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* Array of committed transactions that have modified the catalog.
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*
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* As this array is frequently modified we do *not* keep it in
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* xidComparator order. Instead we sort the array when building &
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* distributing a snapshot.
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*
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* TODO: It's unclear whether that reasoning has much merit. Every
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* time we add something here after becoming consistent will also
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* require distributing a snapshot. Storing them sorted would
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* potentially also make it easier to purge (but more complicated wrt
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* wraparound?). Should be improved if sorting while building the
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* snapshot shows up in profiles.
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*/
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TransactionId *xip;
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} committed;
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/*
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* Array of transactions and subtransactions that had modified catalogs
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* and were running when the snapshot was serialized.
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*
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* We normally rely on some WAL record types such as HEAP2_NEW_CID to know
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* if the transaction has changed the catalog. But it could happen that
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* the logical decoding decodes only the commit record of the transaction
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* after restoring the previously serialized snapshot in which case we
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* will miss adding the xid to the snapshot and end up looking at the
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* catalogs with the wrong snapshot.
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*
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* Now to avoid the above problem, we serialize the transactions that had
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* modified the catalogs and are still running at the time of snapshot
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* serialization. We fill this array while restoring the snapshot and then
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* refer it while decoding commit to ensure if the xact has modified the
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* catalog. We discard this array when all the xids in the list become old
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* enough to matter. See SnapBuildPurgeOlderTxn for details.
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*/
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struct
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{
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/* number of transactions */
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size_t xcnt;
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/* This array must be sorted in xidComparator order */
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TransactionId *xip;
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} catchange;
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};
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/* -----------------------------------
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* Snapshot serialization support
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* -----------------------------------
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*/
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/*
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* We store current state of struct SnapBuild on disk in the following manner:
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*
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* struct SnapBuildOnDisk;
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* TransactionId * committed.xcnt; (*not xcnt_space*)
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* TransactionId * catchange.xcnt;
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*
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* Check if the SnapBuildOnDiskConstantSize and SnapBuildOnDiskNotChecksummedSize
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* macros need to be updated when modifying the SnapBuildOnDisk struct.
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*/
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typedef struct SnapBuildOnDisk
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{
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/* first part of this struct needs to be version independent */
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/* data not covered by checksum */
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uint32 magic;
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pg_crc32c checksum;
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/* data covered by checksum */
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/* version, in case we want to support pg_upgrade */
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uint32 version;
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/* how large is the on disk data, excluding the constant sized part */
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uint32 length;
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/* version dependent part */
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SnapBuild builder;
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/* variable amount of TransactionIds follows */
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} SnapBuildOnDisk;
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extern bool SnapBuildRestoreSnapshot(SnapBuildOnDisk *ondisk, XLogRecPtr lsn,
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MemoryContext context, bool missing_ok);
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#endif /* SNAPBUILD_INTERNAL_H */
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