conflict.c

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/*-------------------------------------------------------------------------
 * conflict.c
 *     Support routines for logging conflicts.
 *
 * Copyright (c) 2024-2025, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *    src/backend/replication/logical/conflict.c
 *
 * This file contains the code for logging conflicts on the subscriber during
 * logical replication.
 *-------------------------------------------------------------------------
 */
 
#include "postgres.h"
 
#include "access/commit_ts.h"
#include "access/tableam.h"
#include "executor/executor.h"
#include "pgstat.h"
#include "replication/conflict.h"
#include "replication/worker_internal.h"
#include "storage/lmgr.h"
#include "utils/lsyscache.h"
 
static const char *const ConflictTypeNames[] = {
    [CT_INSERT_EXISTS] = "insert_exists",
    [CT_UPDATE_ORIGIN_DIFFERS] = "update_origin_differs",
    [CT_UPDATE_EXISTS] = "update_exists",
    [CT_UPDATE_MISSING] = "update_missing",
    [CT_DELETE_ORIGIN_DIFFERS] = "delete_origin_differs",
    [CT_DELETE_MISSING] = "delete_missing",
    [CT_MULTIPLE_UNIQUE_CONFLICTS] = "multiple_unique_conflicts"
};
 
static int  errcode_apply_conflict(ConflictType type);
static void errdetail_apply_conflict(EState *estate,
                                     ResultRelInfo *relinfo,
                                     ConflictType type,
                                     TupleTableSlot *searchslot,
                                     TupleTableSlot *localslot,
                                     TupleTableSlot *remoteslot,
                                     Oid indexoid, TransactionId localxmin,
                                     RepOriginId localorigin,
                                     TimestampTz localts, StringInfo err_msg);
static char *build_tuple_value_details(EState *estate, ResultRelInfo *relinfo,
                                       ConflictType type,
                                       TupleTableSlot *searchslot,
                                       TupleTableSlot *localslot,
                                       TupleTableSlot *remoteslot,
                                       Oid indexoid);
static char *build_index_value_desc(EState *estate, Relation localrel,
                                    TupleTableSlot *slot, Oid indexoid);
 
/*
 * Get the xmin and commit timestamp data (origin and timestamp) associated
 * with the provided local tuple.
 *
 * Return true if the commit timestamp data was found, false otherwise.
 */
bool
GetTupleTransactionInfo(TupleTableSlot *localslot, TransactionId *xmin,
                        RepOriginId *localorigin, TimestampTz *localts)
{
    Datum       xminDatum;
    bool        isnull;
 
    xminDatum = slot_getsysattr(localslot, MinTransactionIdAttributeNumber,
                                &isnull);
    *xmin = DatumGetTransactionId(xminDatum);
    Assert(!isnull);
 
    /*
     * The commit timestamp data is not available if track_commit_timestamp is
     * disabled.
     */
    if (!track_commit_timestamp)
    {
        *localorigin = InvalidRepOriginId;
        *localts = 0;
        return false;
    }
 
    return TransactionIdGetCommitTsData(*xmin, localts, localorigin);
}
 
/*
 * This function is used to report a conflict while applying replication
 * changes.
 *
 * 'searchslot' should contain the tuple used to search the local tuple to be
 * updated or deleted.
 *
 * 'remoteslot' should contain the remote new tuple, if any.
 *
 * conflicttuples is a list of local tuples that caused the conflict and the
 * conflict related information. See ConflictTupleInfo.
 *
 * The caller must ensure that all the indexes passed in ConflictTupleInfo are
 * locked so that we can fetch and display the conflicting key values.
 */
void
ReportApplyConflict(EState *estate, ResultRelInfo *relinfo, int elevel,
                    ConflictType type, TupleTableSlot *searchslot,
                    TupleTableSlot *remoteslot, List *conflicttuples)
{
    Relation    localrel = relinfo->ri_RelationDesc;
    StringInfoData err_detail;
 
    initStringInfo(&err_detail);
 
    /* Form errdetail message by combining conflicting tuples information. */
    foreach_ptr(ConflictTupleInfo, conflicttuple, conflicttuples)
        errdetail_apply_conflict(estate, relinfo, type, searchslot,
                                 conflicttuple->slot, remoteslot,
                                 conflicttuple->indexoid,
                                 conflicttuple->xmin,
                                 conflicttuple->origin,
                                 conflicttuple->ts,
                                 &err_detail);
 
    pgstat_report_subscription_conflict(MySubscription->oid, type);
 
    ereport(elevel,
            errcode_apply_conflict(type),
            errmsg("conflict detected on relation \"%s.%s\": conflict=%s",
                   get_namespace_name(RelationGetNamespace(localrel)),
                   RelationGetRelationName(localrel),
                   ConflictTypeNames[type]),
            errdetail_internal("%s", err_detail.data));
}
 
/*
 * Find all unique indexes to check for a conflict and store them into
 * ResultRelInfo.
 */
void
InitConflictIndexes(ResultRelInfo *relInfo)
{
    List       *uniqueIndexes = NIL;
 
    for (int i = 0; i < relInfo->ri_NumIndices; i++)
    {
        Relation    indexRelation = relInfo->ri_IndexRelationDescs[i];
 
        if (indexRelation == NULL)
            continue;
 
        /* Detect conflict only for unique indexes */
        if (!relInfo->ri_IndexRelationInfo[i]->ii_Unique)
            continue;
 
        /* Don't support conflict detection for deferrable index */
        if (!indexRelation->rd_index->indimmediate)
            continue;
 
        uniqueIndexes = lappend_oid(uniqueIndexes,
                                    RelationGetRelid(indexRelation));
    }
 
    relInfo->ri_onConflictArbiterIndexes = uniqueIndexes;
}
 
/*
 * Add SQLSTATE error code to the current conflict report.
 */
static int
errcode_apply_conflict(ConflictType type)
{
    switch (type)
    {
        case CT_INSERT_EXISTS:
        case CT_UPDATE_EXISTS:
        case CT_MULTIPLE_UNIQUE_CONFLICTS:
            return errcode(ERRCODE_UNIQUE_VIOLATION);
        case CT_UPDATE_ORIGIN_DIFFERS:
        case CT_UPDATE_MISSING:
        case CT_DELETE_ORIGIN_DIFFERS:
        case CT_DELETE_MISSING:
            return errcode(ERRCODE_T_R_SERIALIZATION_FAILURE);
    }
 
    Assert(false);
    return 0;                   /* silence compiler warning */
}
 
/*
 * Add an errdetail() line showing conflict detail.
 *
 * The DETAIL line comprises of two parts:
 * 1. Explanation of the conflict type, including the origin and commit
 *    timestamp of the existing local tuple.
 * 2. Display of conflicting key, existing local tuple, remote new tuple, and
 *    replica identity columns, if any. The remote old tuple is excluded as its
 *    information is covered in the replica identity columns.
 */
static void
errdetail_apply_conflict(EState *estate, ResultRelInfo *relinfo,
                         ConflictType type, TupleTableSlot *searchslot,
                         TupleTableSlot *localslot, TupleTableSlot *remoteslot,
                         Oid indexoid, TransactionId localxmin,
                         RepOriginId localorigin, TimestampTz localts,
                         StringInfo err_msg)
{
    StringInfoData err_detail;
    char       *val_desc;
    char       *origin_name;
 
    initStringInfo(&err_detail);
 
    /* First, construct a detailed message describing the type of conflict */
    switch (type)
    {
        case CT_INSERT_EXISTS:
        case CT_UPDATE_EXISTS:
        case CT_MULTIPLE_UNIQUE_CONFLICTS:
            Assert(OidIsValid(indexoid) &&
                   CheckRelationOidLockedByMe(indexoid, RowExclusiveLock, true));
 
            if (localts)
            {
                if (localorigin == InvalidRepOriginId)
                    appendStringInfo(&err_detail, _("Key already exists in unique index \"%s\", modified locally in transaction %u at %s."),
                                     get_rel_name(indexoid),
                                     localxmin, timestamptz_to_str(localts));
                else if (replorigin_by_oid(localorigin, true, &origin_name))
                    appendStringInfo(&err_detail, _("Key already exists in unique index \"%s\", modified by origin \"%s\" in transaction %u at %s."),
                                     get_rel_name(indexoid), origin_name,
                                     localxmin, timestamptz_to_str(localts));
 
                /*
                 * The origin that modified this row has been removed. This
                 * can happen if the origin was created by a different apply
                 * worker and its associated subscription and origin were
                 * dropped after updating the row, or if the origin was
                 * manually dropped by the user.
                 */
                else
                    appendStringInfo(&err_detail, _("Key already exists in unique index \"%s\", modified by a non-existent origin in transaction %u at %s."),
                                     get_rel_name(indexoid),
                                     localxmin, timestamptz_to_str(localts));
            }
            else
                appendStringInfo(&err_detail, _("Key already exists in unique index \"%s\", modified in transaction %u."),
                                 get_rel_name(indexoid), localxmin);
 
            break;
 
        case CT_UPDATE_ORIGIN_DIFFERS:
            if (localorigin == InvalidRepOriginId)
                appendStringInfo(&err_detail, _("Updating the row that was modified locally in transaction %u at %s."),
                                 localxmin, timestamptz_to_str(localts));
            else if (replorigin_by_oid(localorigin, true, &origin_name))
                appendStringInfo(&err_detail, _("Updating the row that was modified by a different origin \"%s\" in transaction %u at %s."),
                                 origin_name, localxmin, timestamptz_to_str(localts));
 
            /* The origin that modified this row has been removed. */
            else
                appendStringInfo(&err_detail, _("Updating the row that was modified by a non-existent origin in transaction %u at %s."),
                                 localxmin, timestamptz_to_str(localts));
 
            break;
 
        case CT_UPDATE_MISSING:
            appendStringInfo(&err_detail, _("Could not find the row to be updated."));
            break;
 
        case CT_DELETE_ORIGIN_DIFFERS:
            if (localorigin == InvalidRepOriginId)
                appendStringInfo(&err_detail, _("Deleting the row that was modified locally in transaction %u at %s."),
                                 localxmin, timestamptz_to_str(localts));
            else if (replorigin_by_oid(localorigin, true, &origin_name))
                appendStringInfo(&err_detail, _("Deleting the row that was modified by a different origin \"%s\" in transaction %u at %s."),
                                 origin_name, localxmin, timestamptz_to_str(localts));
 
            /* The origin that modified this row has been removed. */
            else
                appendStringInfo(&err_detail, _("Deleting the row that was modified by a non-existent origin in transaction %u at %s."),
                                 localxmin, timestamptz_to_str(localts));
 
            break;
 
        case CT_DELETE_MISSING:
            appendStringInfo(&err_detail, _("Could not find the row to be deleted."));
            break;
    }
 
    Assert(err_detail.len > 0);
 
    val_desc = build_tuple_value_details(estate, relinfo, type, searchslot,
                                         localslot, remoteslot, indexoid);
 
    /*
     * Next, append the key values, existing local tuple, remote tuple and
     * replica identity columns after the message.
     */
    if (val_desc)
        appendStringInfo(&err_detail, "\n%s", val_desc);
 
    /*
     * Insert a blank line to visually separate the new detail line from the
     * existing ones.
     */
    if (err_msg->len > 0)
        appendStringInfoChar(err_msg, '\n');
 
    appendStringInfo(err_msg, "%s", err_detail.data);
}
 
/*
 * Helper function to build the additional details for conflicting key,
 * existing local tuple, remote tuple, and replica identity columns.
 *
 * If the return value is NULL, it indicates that the current user lacks
 * permissions to view the columns involved.
 */
static char *
build_tuple_value_details(EState *estate, ResultRelInfo *relinfo,
                          ConflictType type,
                          TupleTableSlot *searchslot,
                          TupleTableSlot *localslot,
                          TupleTableSlot *remoteslot,
                          Oid indexoid)
{
    Relation    localrel = relinfo->ri_RelationDesc;
    Oid         relid = RelationGetRelid(localrel);
    TupleDesc   tupdesc = RelationGetDescr(localrel);
    StringInfoData tuple_value;
    char       *desc = NULL;
 
    Assert(searchslot || localslot || remoteslot);
 
    initStringInfo(&tuple_value);
 
    /*
     * Report the conflicting key values in the case of a unique constraint
     * violation.
     */
    if (type == CT_INSERT_EXISTS || type == CT_UPDATE_EXISTS ||
        type == CT_MULTIPLE_UNIQUE_CONFLICTS)
    {
        Assert(OidIsValid(indexoid) && localslot);
 
        desc = build_index_value_desc(estate, localrel, localslot, indexoid);
 
        if (desc)
            appendStringInfo(&tuple_value, _("Key %s"), desc);
    }
 
    if (localslot)
    {
        /*
         * The 'modifiedCols' only applies to the new tuple, hence we pass
         * NULL for the existing local tuple.
         */
        desc = ExecBuildSlotValueDescription(relid, localslot, tupdesc,
                                             NULL, 64);
 
        if (desc)
        {
            if (tuple_value.len > 0)
            {
                appendStringInfoString(&tuple_value, "; ");
                appendStringInfo(&tuple_value, _("existing local tuple %s"),
                                 desc);
            }
            else
            {
                appendStringInfo(&tuple_value, _("Existing local tuple %s"),
                                 desc);
            }
        }
    }
 
    if (remoteslot)
    {
        Bitmapset  *modifiedCols;
 
        /*
         * Although logical replication doesn't maintain the bitmap for the
         * columns being inserted, we still use it to create 'modifiedCols'
         * for consistency with other calls to ExecBuildSlotValueDescription.
         *
         * Note that generated columns are formed locally on the subscriber.
         */
        modifiedCols = bms_union(ExecGetInsertedCols(relinfo, estate),
                                 ExecGetUpdatedCols(relinfo, estate));
        desc = ExecBuildSlotValueDescription(relid, remoteslot, tupdesc,
                                             modifiedCols, 64);
 
        if (desc)
        {
            if (tuple_value.len > 0)
            {
                appendStringInfoString(&tuple_value, "; ");
                appendStringInfo(&tuple_value, _("remote tuple %s"), desc);
            }
            else
            {
                appendStringInfo(&tuple_value, _("Remote tuple %s"), desc);
            }
        }
    }
 
    if (searchslot)
    {
        /*
         * Note that while index other than replica identity may be used (see
         * IsIndexUsableForReplicaIdentityFull for details) to find the tuple
         * when applying update or delete, such an index scan may not result
         * in a unique tuple and we still compare the complete tuple in such
         * cases, thus such indexes are not used here.
         */
        Oid         replica_index = GetRelationIdentityOrPK(localrel);
 
        Assert(type != CT_INSERT_EXISTS);
 
        /*
         * If the table has a valid replica identity index, build the index
         * key value string. Otherwise, construct the full tuple value for
         * REPLICA IDENTITY FULL cases.
         */
        if (OidIsValid(replica_index))
            desc = build_index_value_desc(estate, localrel, searchslot, replica_index);
        else
            desc = ExecBuildSlotValueDescription(relid, searchslot, tupdesc, NULL, 64);
 
        if (desc)
        {
            if (tuple_value.len > 0)
            {
                appendStringInfoString(&tuple_value, "; ");
                appendStringInfo(&tuple_value, OidIsValid(replica_index)
                                 ? _("replica identity %s")
                                 : _("replica identity full %s"), desc);
            }
            else
            {
                appendStringInfo(&tuple_value, OidIsValid(replica_index)
                                 ? _("Replica identity %s")
                                 : _("Replica identity full %s"), desc);
            }
        }
    }
 
    if (tuple_value.len == 0)
        return NULL;
 
    appendStringInfoChar(&tuple_value, '.');
    return tuple_value.data;
}
 
/*
 * Helper functions to construct a string describing the contents of an index
 * entry. See BuildIndexValueDescription for details.
 *
 * The caller must ensure that the index with the OID 'indexoid' is locked so
 * that we can fetch and display the conflicting key value.
 */
static char *
build_index_value_desc(EState *estate, Relation localrel, TupleTableSlot *slot,
                       Oid indexoid)
{
    char       *index_value;
    Relation    indexDesc;
    Datum       values[INDEX_MAX_KEYS];
    bool        isnull[INDEX_MAX_KEYS];
    TupleTableSlot *tableslot = slot;
 
    if (!tableslot)
        return NULL;
 
    Assert(CheckRelationOidLockedByMe(indexoid, RowExclusiveLock, true));
 
    indexDesc = index_open(indexoid, NoLock);
 
    /*
     * If the slot is a virtual slot, copy it into a heap tuple slot as
     * FormIndexDatum only works with heap tuple slots.
     */
    if (TTS_IS_VIRTUAL(slot))
    {
        tableslot = table_slot_create(localrel, &estate->es_tupleTable);
        tableslot = ExecCopySlot(tableslot, slot);
    }
 
    /*
     * Initialize ecxt_scantuple for potential use in FormIndexDatum when
     * index expressions are present.
     */
    GetPerTupleExprContext(estate)->ecxt_scantuple = tableslot;
 
    /*
     * The values/nulls arrays passed to BuildIndexValueDescription should be
     * the results of FormIndexDatum, which are the "raw" input to the index
     * AM.
     */
    FormIndexDatum(BuildIndexInfo(indexDesc), tableslot, estate, values, isnull);
 
    index_value = BuildIndexValueDescription(indexDesc, values, isnull);
 
    index_close(indexDesc, NoLock);
 
    return index_value;
}