info.c

Go to the documentation of this file.

/*
 *  info.c
 *
 *  information support functions
 *
 *  Copyright (c) 2010-2026, PostgreSQL Global Development Group
 *  src/bin/pg_upgrade/info.c
 */
 
#include "postgres_fe.h"
 
#include "access/transam.h"
#include "catalog/pg_class_d.h"
#include "pg_upgrade.h"
#include "pqexpbuffer.h"
 
static void create_rel_filename_map(const char *old_data, const char *new_data,
                                    const DbInfo *old_db, const DbInfo *new_db,
                                    const RelInfo *old_rel, const RelInfo *new_rel,
                                    FileNameMap *map);
static void report_unmatched_relation(const RelInfo *rel, const DbInfo *db,
                                      bool is_new_db);
static void free_db_and_rel_infos(DbInfoArr *db_arr);
static void get_template0_info(ClusterInfo *cluster);
static void get_db_infos(ClusterInfo *cluster);
static char *get_rel_infos_query(void);
static void process_rel_infos(DbInfo *dbinfo, PGresult *res, void *arg);
static void free_rel_infos(RelInfoArr *rel_arr);
static void print_db_infos(DbInfoArr *db_arr);
static void print_rel_infos(RelInfoArr *rel_arr);
static void print_slot_infos(LogicalSlotInfoArr *slot_arr);
static const char *get_old_cluster_logical_slot_infos_query(ClusterInfo *cluster);
static void process_old_cluster_logical_slot_infos(DbInfo *dbinfo, PGresult *res, void *arg);
 
 
/*
 * gen_db_file_maps()
 *
 * generates a database mapping from "old_db" to "new_db".
 *
 * Returns a malloc'ed array of mappings.  The length of the array
 * is returned into *nmaps.
 */
FileNameMap *
gen_db_file_maps(DbInfo *old_db, DbInfo *new_db,
                 int *nmaps,
                 const char *old_pgdata, const char *new_pgdata)
{
    FileNameMap *maps;
    int         old_relnum,
                new_relnum;
    int         num_maps = 0;
    bool        all_matched = true;
 
    /* There will certainly not be more mappings than there are old rels */
    maps = pg_malloc_array(FileNameMap, old_db->rel_arr.nrels);
 
    /*
     * Each of the RelInfo arrays should be sorted by OID.  Scan through them
     * and match them up.  If we fail to match everything, we'll abort, but
     * first print as much info as we can about mismatches.
     */
    old_relnum = new_relnum = 0;
    while (old_relnum < old_db->rel_arr.nrels ||
           new_relnum < new_db->rel_arr.nrels)
    {
        RelInfo    *old_rel = (old_relnum < old_db->rel_arr.nrels) ?
            &old_db->rel_arr.rels[old_relnum] : NULL;
        RelInfo    *new_rel = (new_relnum < new_db->rel_arr.nrels) ?
            &new_db->rel_arr.rels[new_relnum] : NULL;
 
        /* handle running off one array before the other */
        if (!new_rel)
        {
            /*
             * old_rel is unmatched.  This should never happen, because we
             * force new rels to have TOAST tables if the old one did.
             */
            report_unmatched_relation(old_rel, old_db, false);
            all_matched = false;
            old_relnum++;
            continue;
        }
        if (!old_rel)
        {
            /*
             * new_rel is unmatched.  This shouldn't really happen either, but
             * if it's a TOAST table, we can ignore it and continue
             * processing, assuming that the new server made a TOAST table
             * that wasn't needed.
             */
            if (strcmp(new_rel->nspname, "pg_toast") != 0)
            {
                report_unmatched_relation(new_rel, new_db, true);
                all_matched = false;
            }
            new_relnum++;
            continue;
        }
 
        /* check for mismatched OID */
        if (old_rel->reloid < new_rel->reloid)
        {
            /* old_rel is unmatched, see comment above */
            report_unmatched_relation(old_rel, old_db, false);
            all_matched = false;
            old_relnum++;
            continue;
        }
        else if (old_rel->reloid > new_rel->reloid)
        {
            /* new_rel is unmatched, see comment above */
            if (strcmp(new_rel->nspname, "pg_toast") != 0)
            {
                report_unmatched_relation(new_rel, new_db, true);
                all_matched = false;
            }
            new_relnum++;
            continue;
        }
 
        /*
         * Verify that rels of same OID have same name.  The namespace name
         * should always match, but the relname might not match for TOAST
         * tables (and, therefore, their indexes).
         */
        if (strcmp(old_rel->nspname, new_rel->nspname) != 0 ||
            strcmp(old_rel->relname, new_rel->relname) != 0)
        {
            pg_log(PG_WARNING, "Relation names for OID %u in database \"%s\" do not match: "
                   "old name \"%s.%s\", new name \"%s.%s\"",
                   old_rel->reloid, old_db->db_name,
                   old_rel->nspname, old_rel->relname,
                   new_rel->nspname, new_rel->relname);
            all_matched = false;
            old_relnum++;
            new_relnum++;
            continue;
        }
 
        /* OK, create a mapping entry */
        create_rel_filename_map(old_pgdata, new_pgdata, old_db, new_db,
                                old_rel, new_rel, maps + num_maps);
        num_maps++;
        old_relnum++;
        new_relnum++;
    }
 
    if (!all_matched)
        pg_fatal("Failed to match up old and new tables in database \"%s\"",
                 old_db->db_name);
 
    *nmaps = num_maps;
    return maps;
}
 
 
/*
 * create_rel_filename_map()
 *
 * fills a file node map structure and returns it in "map".
 */
static void
create_rel_filename_map(const char *old_data, const char *new_data,
                        const DbInfo *old_db, const DbInfo *new_db,
                        const RelInfo *old_rel, const RelInfo *new_rel,
                        FileNameMap *map)
{
    /* In case old/new tablespaces don't match, do them separately. */
    if (strlen(old_rel->tablespace) == 0)
    {
        /*
         * relation belongs to the default tablespace, hence relfiles should
         * exist in the data directories.
         */
        map->old_tablespace = old_data;
        map->old_tablespace_suffix = "/base";
    }
    else
    {
        /* relation belongs to a tablespace, so use the tablespace location */
        map->old_tablespace = old_rel->tablespace;
        map->old_tablespace_suffix = old_cluster.tablespace_suffix;
    }
 
    /* Do the same for new tablespaces */
    if (strlen(new_rel->tablespace) == 0)
    {
        map->new_tablespace = new_data;
        map->new_tablespace_suffix = "/base";
    }
    else
    {
        map->new_tablespace = new_rel->tablespace;
        map->new_tablespace_suffix = new_cluster.tablespace_suffix;
    }
 
    /* DB oid and relfilenumbers are preserved between old and new cluster */
    map->db_oid = old_db->db_oid;
    map->relfilenumber = old_rel->relfilenumber;
 
    /* used only for logging and error reporting, old/new are identical */
    map->nspname = old_rel->nspname;
    map->relname = old_rel->relname;
}
 
 
/*
 * Complain about a relation we couldn't match to the other database,
 * identifying it as best we can.
 */
static void
report_unmatched_relation(const RelInfo *rel, const DbInfo *db, bool is_new_db)
{
    Oid         reloid = rel->reloid;   /* we might change rel below */
    char        reldesc[1000];
    int         i;
 
    snprintf(reldesc, sizeof(reldesc), "\"%s.%s\"",
             rel->nspname, rel->relname);
    if (rel->indtable)
    {
        for (i = 0; i < db->rel_arr.nrels; i++)
        {
            const RelInfo *hrel = &db->rel_arr.rels[i];
 
            if (hrel->reloid == rel->indtable)
            {
                snprintf(reldesc + strlen(reldesc),
                         sizeof(reldesc) - strlen(reldesc),
                         _(" which is an index on \"%s.%s\""),
                         hrel->nspname, hrel->relname);
                /* Shift attention to index's table for toast check */
                rel = hrel;
                break;
            }
        }
        if (i >= db->rel_arr.nrels)
            snprintf(reldesc + strlen(reldesc),
                     sizeof(reldesc) - strlen(reldesc),
                     _(" which is an index on OID %u"), rel->indtable);
    }
    if (rel->toastheap)
    {
        for (i = 0; i < db->rel_arr.nrels; i++)
        {
            const RelInfo *brel = &db->rel_arr.rels[i];
 
            if (brel->reloid == rel->toastheap)
            {
                snprintf(reldesc + strlen(reldesc),
                         sizeof(reldesc) - strlen(reldesc),
                         _(" which is the TOAST table for \"%s.%s\""),
                         brel->nspname, brel->relname);
                break;
            }
        }
        if (i >= db->rel_arr.nrels)
            snprintf(reldesc + strlen(reldesc),
                     sizeof(reldesc) - strlen(reldesc),
                     _(" which is the TOAST table for OID %u"), rel->toastheap);
    }
 
    if (is_new_db)
        pg_log(PG_WARNING, "No match found in old cluster for new relation with OID %u in database \"%s\": %s",
               reloid, db->db_name, reldesc);
    else
        pg_log(PG_WARNING, "No match found in new cluster for old relation with OID %u in database \"%s\": %s",
               reloid, db->db_name, reldesc);
}
 
/*
 * get_db_rel_and_slot_infos()
 *
 * higher level routine to generate dbinfos for the database running
 * on the given "port". Assumes that server is already running.
 */
void
get_db_rel_and_slot_infos(ClusterInfo *cluster)
{
    UpgradeTask *task = upgrade_task_create();
    char       *rel_infos_query = NULL;
 
    if (cluster->dbarr.dbs != NULL)
        free_db_and_rel_infos(&cluster->dbarr);
 
    get_template0_info(cluster);
    get_db_infos(cluster);
 
    rel_infos_query = get_rel_infos_query();
    upgrade_task_add_step(task,
                          rel_infos_query,
                          process_rel_infos,
                          true, NULL);
 
    /*
     * Logical slots are only carried over to the new cluster when the old
     * cluster is on PG17 or newer.  This is because before that the logical
     * slots are not saved at shutdown, so there is no guarantee that the
     * latest confirmed_flush_lsn is saved to disk which can lead to data
     * loss. It is still not guaranteed for manually created slots in PG17, so
     * subsequent checks done in check_old_cluster_for_valid_slots() would
     * raise a FATAL error if such slots are included.
     */
    if (cluster == &old_cluster &&
        GET_MAJOR_VERSION(cluster->major_version) > 1600)
        upgrade_task_add_step(task,
                              get_old_cluster_logical_slot_infos_query(cluster),
                              process_old_cluster_logical_slot_infos,
                              true, NULL);
 
    upgrade_task_run(task, cluster);
    upgrade_task_free(task);
 
    pg_free(rel_infos_query);
 
    if (cluster == &old_cluster)
        pg_log(PG_VERBOSE, "\nsource databases:");
    else
        pg_log(PG_VERBOSE, "\ntarget databases:");
 
    if (log_opts.verbose)
        print_db_infos(&cluster->dbarr);
}
 
 
/*
 * Get information about template0, which will be copied from the old cluster
 * to the new cluster.
 */
static void
get_template0_info(ClusterInfo *cluster)
{
    PGconn     *conn = connectToServer(cluster, "template1");
    DbLocaleInfo *locale;
    PGresult   *dbres;
    int         i_datencoding;
    int         i_datlocprovider;
    int         i_datcollate;
    int         i_datctype;
    int         i_datlocale;
 
    if (GET_MAJOR_VERSION(cluster->major_version) >= 1700)
        dbres = executeQueryOrDie(conn,
                                  "SELECT encoding, datlocprovider, "
                                  "       datcollate, datctype, datlocale "
                                  "FROM pg_catalog.pg_database "
                                  "WHERE datname='template0'");
    else if (GET_MAJOR_VERSION(cluster->major_version) >= 1500)
        dbres = executeQueryOrDie(conn,
                                  "SELECT encoding, datlocprovider, "
                                  "       datcollate, datctype, daticulocale AS datlocale "
                                  "FROM pg_catalog.pg_database "
                                  "WHERE datname='template0'");
    else
        dbres = executeQueryOrDie(conn,
                                  "SELECT encoding, 'c' AS datlocprovider, "
                                  "       datcollate, datctype, NULL AS datlocale "
                                  "FROM pg_catalog.pg_database "
                                  "WHERE datname='template0'");
 
 
    if (PQntuples(dbres) != 1)
        pg_fatal("template0 not found");
 
    locale = pg_malloc_object(DbLocaleInfo);
 
    i_datencoding = PQfnumber(dbres, "encoding");
    i_datlocprovider = PQfnumber(dbres, "datlocprovider");
    i_datcollate = PQfnumber(dbres, "datcollate");
    i_datctype = PQfnumber(dbres, "datctype");
    i_datlocale = PQfnumber(dbres, "datlocale");
 
    locale->db_encoding = atoi(PQgetvalue(dbres, 0, i_datencoding));
    locale->db_collprovider = PQgetvalue(dbres, 0, i_datlocprovider)[0];
    locale->db_collate = pg_strdup(PQgetvalue(dbres, 0, i_datcollate));
    locale->db_ctype = pg_strdup(PQgetvalue(dbres, 0, i_datctype));
    if (PQgetisnull(dbres, 0, i_datlocale))
        locale->db_locale = NULL;
    else
        locale->db_locale = pg_strdup(PQgetvalue(dbres, 0, i_datlocale));
 
    cluster->template0 = locale;
 
    PQclear(dbres);
    PQfinish(conn);
}
 
 
/*
 * get_db_infos()
 *
 * Scans pg_database system catalog and populates all user
 * databases.
 */
static void
get_db_infos(ClusterInfo *cluster)
{
    PGconn     *conn = connectToServer(cluster, "template1");
    PGresult   *res;
    int         ntups;
    int         tupnum;
    DbInfo     *dbinfos;
    int         i_datname,
                i_oid,
                i_spclocation;
    char        query[QUERY_ALLOC];
 
    snprintf(query, sizeof(query),
             "SELECT d.oid, d.datname, d.encoding, d.datcollate, d.datctype, ");
    if (GET_MAJOR_VERSION(cluster->major_version) >= 1700)
        snprintf(query + strlen(query), sizeof(query) - strlen(query),
                 "datlocprovider, datlocale, ");
    else if (GET_MAJOR_VERSION(cluster->major_version) >= 1500)
        snprintf(query + strlen(query), sizeof(query) - strlen(query),
                 "datlocprovider, daticulocale AS datlocale, ");
    else
        snprintf(query + strlen(query), sizeof(query) - strlen(query),
                 "'c' AS datlocprovider, NULL AS datlocale, ");
    snprintf(query + strlen(query), sizeof(query) - strlen(query),
             "pg_catalog.pg_tablespace_location(t.oid) AS spclocation "
             "FROM pg_catalog.pg_database d "
             " LEFT OUTER JOIN pg_catalog.pg_tablespace t "
             " ON d.dattablespace = t.oid "
             "WHERE d.datallowconn = true "
             "ORDER BY 1");
 
    res = executeQueryOrDie(conn, "%s", query);
 
    i_oid = PQfnumber(res, "oid");
    i_datname = PQfnumber(res, "datname");
    i_spclocation = PQfnumber(res, "spclocation");
 
    ntups = PQntuples(res);
    dbinfos = pg_malloc0_array(DbInfo, ntups);
 
    for (tupnum = 0; tupnum < ntups; tupnum++)
    {
        char       *spcloc = PQgetvalue(res, tupnum, i_spclocation);
        bool        inplace = spcloc[0] && !is_absolute_path(spcloc);
 
        dbinfos[tupnum].db_oid = atooid(PQgetvalue(res, tupnum, i_oid));
        dbinfos[tupnum].db_name = pg_strdup(PQgetvalue(res, tupnum, i_datname));
 
        /*
         * The tablespace location might be "", meaning the cluster default
         * location, i.e. pg_default or pg_global.  For in-place tablespaces,
         * pg_tablespace_location() returns a path relative to the data
         * directory.
         */
        if (inplace)
            snprintf(dbinfos[tupnum].db_tablespace,
                     sizeof(dbinfos[tupnum].db_tablespace),
                     "%s/%s", cluster->pgdata, spcloc);
        else
            snprintf(dbinfos[tupnum].db_tablespace,
                     sizeof(dbinfos[tupnum].db_tablespace),
                     "%s", spcloc);
    }
    PQclear(res);
 
    PQfinish(conn);
 
    cluster->dbarr.dbs = dbinfos;
    cluster->dbarr.ndbs = ntups;
}
 
 
/*
 * get_rel_infos_query()
 *
 * Returns the query for retrieving the relation information for all the user
 * tables and indexes in the database, for use by get_db_rel_and_slot_infos()'s
 * UpgradeTask.
 *
 * Note: the result is assumed to be sorted by OID.  This allows later
 * processing to match up old and new databases efficiently.
 */
static char *
get_rel_infos_query(void)
{
    PQExpBufferData query;
 
    initPQExpBuffer(&query);
 
    /*
     * Create a CTE that collects OIDs of regular user tables and matviews,
     * but excluding toast tables and indexes.  We assume that relations with
     * OIDs >= FirstNormalObjectId belong to the user.  (That's probably
     * redundant with the namespace-name exclusions, but let's be safe.)
     *
     * pg_largeobject contains user data that does not appear in pg_dump
     * output, so we have to copy that system table.  It's easiest to do that
     * by treating it as a user table.  We can do the same for
     * pg_largeobject_metadata for upgrades from v16 and newer.  pg_upgrade
     * can't copy/link the files from older versions because aclitem (needed
     * by pg_largeobject_metadata.lomacl) changed its storage format in v16.
     */
    appendPQExpBuffer(&query,
                      "WITH regular_heap (reloid, indtable, toastheap) AS ( "
                      "  SELECT c.oid, 0::oid, 0::oid "
                      "  FROM pg_catalog.pg_class c JOIN pg_catalog.pg_namespace n "
                      "         ON c.relnamespace = n.oid "
                      "  WHERE relkind IN (" CppAsString2(RELKIND_RELATION) ", "
                      CppAsString2(RELKIND_MATVIEW) "%s) AND "
    /* exclude possible orphaned temp tables */
                      "    ((n.nspname !~ '^pg_temp_' AND "
                      "      n.nspname !~ '^pg_toast_temp_' AND "
                      "      n.nspname NOT IN ('pg_catalog', 'information_schema', "
                      "                        'binary_upgrade', 'pg_toast') AND "
                      "      c.oid >= %u::pg_catalog.oid) OR "
                      "     (n.nspname = 'pg_catalog' AND "
                      "      relname IN ('pg_largeobject'%s) ))), ",
                      (user_opts.transfer_mode == TRANSFER_MODE_SWAP) ?
                      ", " CppAsString2(RELKIND_SEQUENCE) : "",
                      FirstNormalObjectId,
                      (GET_MAJOR_VERSION(old_cluster.major_version) >= 1600) ?
                      ", 'pg_largeobject_metadata'" : "");
 
    /*
     * Add a CTE that collects OIDs of toast tables belonging to the tables
     * selected by the regular_heap CTE.  (We have to do this separately
     * because the namespace-name rules above don't work for toast tables.)
     */
    appendPQExpBufferStr(&query,
                         "  toast_heap (reloid, indtable, toastheap) AS ( "
                         "  SELECT c.reltoastrelid, 0::oid, c.oid "
                         "  FROM regular_heap JOIN pg_catalog.pg_class c "
                         "      ON regular_heap.reloid = c.oid "
                         "  WHERE c.reltoastrelid != 0), ");
 
    /*
     * Add a CTE that collects OIDs of all valid indexes on the previously
     * selected tables.  We can ignore invalid indexes since pg_dump does.
     * Testing indisready is necessary in 9.2, and harmless in earlier/later
     * versions.
     */
    appendPQExpBufferStr(&query,
                         "  all_index (reloid, indtable, toastheap) AS ( "
                         "  SELECT indexrelid, indrelid, 0::oid "
                         "  FROM pg_catalog.pg_index "
                         "  WHERE indisvalid AND indisready "
                         "    AND indrelid IN "
                         "        (SELECT reloid FROM regular_heap "
                         "         UNION ALL "
                         "         SELECT reloid FROM toast_heap)) ");
 
    /*
     * And now we can write the query that retrieves the data we want for each
     * heap and index relation.  Make sure result is sorted by OID.
     */
    appendPQExpBufferStr(&query,
                         "SELECT all_rels.*, n.nspname, c.relname, "
                         "  c.relfilenode, c.reltablespace, "
                         "  pg_catalog.pg_tablespace_location(t.oid) AS spclocation "
                         "FROM (SELECT * FROM regular_heap "
                         "      UNION ALL "
                         "      SELECT * FROM toast_heap "
                         "      UNION ALL "
                         "      SELECT * FROM all_index) all_rels "
                         "  JOIN pg_catalog.pg_class c "
                         "      ON all_rels.reloid = c.oid "
                         "  JOIN pg_catalog.pg_namespace n "
                         "     ON c.relnamespace = n.oid "
                         "  LEFT OUTER JOIN pg_catalog.pg_tablespace t "
                         "     ON c.reltablespace = t.oid "
                         "ORDER BY 1");
 
    return query.data;
}
 
/*
 * Callback function for processing results of the query returned by
 * get_rel_infos_query(), which is used for get_db_rel_and_slot_infos()'s
 * UpgradeTask.  This function stores the relation information for later use.
 */
static void
process_rel_infos(DbInfo *dbinfo, PGresult *res, void *arg)
{
    int         ntups = PQntuples(res);
    RelInfo    *relinfos = pg_malloc_array(RelInfo, ntups);
    int         i_reloid = PQfnumber(res, "reloid");
    int         i_indtable = PQfnumber(res, "indtable");
    int         i_toastheap = PQfnumber(res, "toastheap");
    int         i_nspname = PQfnumber(res, "nspname");
    int         i_relname = PQfnumber(res, "relname");
    int         i_relfilenumber = PQfnumber(res, "relfilenode");
    int         i_reltablespace = PQfnumber(res, "reltablespace");
    int         i_spclocation = PQfnumber(res, "spclocation");
    int         num_rels = 0;
    char       *nspname = NULL;
    char       *relname = NULL;
    char       *tablespace = NULL;
    char       *last_namespace = NULL;
    char       *last_tablespace = NULL;
 
    for (int relnum = 0; relnum < ntups; relnum++)
    {
        RelInfo    *curr = &relinfos[num_rels++];
 
        curr->reloid = atooid(PQgetvalue(res, relnum, i_reloid));
        curr->indtable = atooid(PQgetvalue(res, relnum, i_indtable));
        curr->toastheap = atooid(PQgetvalue(res, relnum, i_toastheap));
 
        nspname = PQgetvalue(res, relnum, i_nspname);
        curr->nsp_alloc = false;
 
        /*
         * Many of the namespace and tablespace strings are identical, so we
         * try to reuse the allocated string pointers where possible to reduce
         * memory consumption.
         */
        /* Can we reuse the previous string allocation? */
        if (last_namespace && strcmp(nspname, last_namespace) == 0)
            curr->nspname = last_namespace;
        else
        {
            last_namespace = curr->nspname = pg_strdup(nspname);
            curr->nsp_alloc = true;
        }
 
        relname = PQgetvalue(res, relnum, i_relname);
        curr->relname = pg_strdup(relname);
 
        curr->relfilenumber = atooid(PQgetvalue(res, relnum, i_relfilenumber));
        curr->tblsp_alloc = false;
 
        /* Is the tablespace oid non-default? */
        if (atooid(PQgetvalue(res, relnum, i_reltablespace)) != 0)
        {
            char       *spcloc = PQgetvalue(res, relnum, i_spclocation);
            bool        inplace = spcloc[0] && !is_absolute_path(spcloc);
 
            /*
             * The tablespace location might be "", meaning the cluster
             * default location, i.e. pg_default or pg_global.  For in-place
             * tablespaces, pg_tablespace_location() returns a path relative
             * to the data directory.
             */
            if (inplace)
                tablespace = psprintf("%s/%s",
                                      os_info.running_cluster->pgdata,
                                      spcloc);
            else
                tablespace = spcloc;
 
            /* Can we reuse the previous string allocation? */
            if (last_tablespace && strcmp(tablespace, last_tablespace) == 0)
                curr->tablespace = last_tablespace;
            else
            {
                last_tablespace = curr->tablespace = pg_strdup(tablespace);
                curr->tblsp_alloc = true;
            }
 
            /* Free palloc'd string for in-place tablespaces. */
            if (inplace)
                pfree(tablespace);
        }
        else
            /* A zero reltablespace oid indicates the database tablespace. */
            curr->tablespace = dbinfo->db_tablespace;
    }
 
    dbinfo->rel_arr.rels = relinfos;
    dbinfo->rel_arr.nrels = num_rels;
}
 
/*
 * get_old_cluster_logical_slot_infos_query()
 *
 * Returns the query for retrieving the logical slot information for all the
 * logical replication slots in the database, for use by
 * get_db_rel_and_slot_infos()'s UpgradeTask.  The status of each logical slot
 * is checked in check_old_cluster_for_valid_slots().
 */
static const char *
get_old_cluster_logical_slot_infos_query(ClusterInfo *cluster)
{
    /*
     * Fetch the logical replication slot information. The check whether the
     * slot is considered caught up is done by an upgrade function. This
     * regards the slot as caught up if we don't find any decodable changes.
     * The implementation of this check varies depending on the server
     * version.
     *
     * We intentionally skip checking the WALs for invalidated slots as the
     * corresponding WALs could have been removed for such slots.
     *
     * The temporary slots are explicitly ignored while checking because such
     * slots cannot exist after the upgrade. During the upgrade, clusters are
     * started and stopped several times causing any temporary slots to be
     * removed.
     */
 
    if (user_opts.live_check)
    {
        /*
         * We skip the caught-up check during live_check. We cannot verify
         * whether the slot is caught up in this mode, as new WAL records
         * could be generated concurrently.
         */
        return "SELECT slot_name, plugin, two_phase, failover, "
            "FALSE as caught_up, "
            "invalidation_reason IS NOT NULL as invalid "
            "FROM pg_catalog.pg_replication_slots "
            "WHERE slot_type = 'logical' AND "
            "database = current_database() AND "
            "temporary IS FALSE";
    }
    else if (GET_MAJOR_VERSION(cluster->major_version) >= 1900)
    {
        /*
         * For PG19 and later, we optimize the slot caught-up check to avoid
         * reading the same WAL stream multiple times: execute the caught-up
         * check only for the slot with the minimum confirmed_flush_lsn, and
         * apply the same result to all other slots in the same database. This
         * limits the check to at most one logical slot per database. We also
         * use the maximum confirmed_flush_lsn among all logical slots on the
         * database as an early scan cutoff; finding a decodable WAL record
         * beyond this point implies that no slot has caught up.
         *
         * Note that we don't distinguish slots based on their output plugin.
         * If a plugin applies replication origin filters, we might get a
         * false positive (i.e., erroneously considering a slot caught up).
         * However, such cases are very rare, and the impact of a false
         * positive is minimal.
         */
        return "WITH check_caught_up AS ( "
            "  SELECT pg_catalog.binary_upgrade_check_logical_slot_pending_wal(slot_name, "
            "    MAX(confirmed_flush_lsn) OVER ()) as last_pending_wal "
            "  FROM pg_replication_slots "
            "  WHERE slot_type = 'logical' AND "
            "    database = current_database() AND "
            "    temporary IS FALSE AND "
            "    invalidation_reason IS NULL "
            "  ORDER BY confirmed_flush_lsn ASC "
            "  LIMIT 1 "
            ") "
            "SELECT slot_name, plugin, two_phase, failover, "
            "CASE WHEN invalidation_reason IS NOT NULL THEN FALSE "
            "ELSE  last_pending_wal IS NULL OR "
            "  confirmed_flush_lsn > last_pending_wal "
            "END as caught_up, "
            "invalidation_reason IS NOT NULL as invalid "
            "FROM pg_catalog.pg_replication_slots, check_caught_up "
            "WHERE slot_type = 'logical' AND "
            "database = current_database() AND "
            "temporary IS FALSE ";
    }
 
    /*
     * For PG18 and earlier, we call
     * binary_upgrade_logical_slot_has_caught_up() for each logical slot.
     */
    return "SELECT slot_name, plugin, two_phase, failover, "
        "CASE WHEN invalidation_reason IS NOT NULL THEN FALSE "
        "ELSE (SELECT pg_catalog.binary_upgrade_logical_slot_has_caught_up(slot_name)) "
        "END as caught_up, "
        "invalidation_reason IS NOT NULL as invalid "
        "FROM pg_catalog.pg_replication_slots "
        "WHERE slot_type = 'logical' AND "
        "database = current_database() AND "
        "temporary IS FALSE ";
}
 
/*
 * Callback function for processing results of the query, which is used for
 * get_db_rel_and_slot_infos()'s UpgradeTask.  This function stores the logical
 * slot information for later use.
 */
static void
process_old_cluster_logical_slot_infos(DbInfo *dbinfo, PGresult *res, void *arg)
{
    LogicalSlotInfo *slotinfos = NULL;
    int         num_slots = PQntuples(res);
 
    if (num_slots)
    {
        int         i_slotname;
        int         i_plugin;
        int         i_twophase;
        int         i_failover;
        int         i_caught_up;
        int         i_invalid;
 
        slotinfos = pg_malloc_array(LogicalSlotInfo, num_slots);
 
        i_slotname = PQfnumber(res, "slot_name");
        i_plugin = PQfnumber(res, "plugin");
        i_twophase = PQfnumber(res, "two_phase");
        i_failover = PQfnumber(res, "failover");
        i_caught_up = PQfnumber(res, "caught_up");
        i_invalid = PQfnumber(res, "invalid");
 
        for (int slotnum = 0; slotnum < num_slots; slotnum++)
        {
            LogicalSlotInfo *curr = &slotinfos[slotnum];
 
            curr->slotname = pg_strdup(PQgetvalue(res, slotnum, i_slotname));
            curr->plugin = pg_strdup(PQgetvalue(res, slotnum, i_plugin));
            curr->two_phase = (strcmp(PQgetvalue(res, slotnum, i_twophase), "t") == 0);
            curr->failover = (strcmp(PQgetvalue(res, slotnum, i_failover), "t") == 0);
            curr->caught_up = (strcmp(PQgetvalue(res, slotnum, i_caught_up), "t") == 0);
            curr->invalid = (strcmp(PQgetvalue(res, slotnum, i_invalid), "t") == 0);
        }
    }
 
    dbinfo->slot_arr.slots = slotinfos;
    dbinfo->slot_arr.nslots = num_slots;
}
 
 
/*
 * count_old_cluster_logical_slots()
 *
 * Returns the number of logical replication slots for all databases.
 *
 * Note: this function always returns 0 if the old_cluster is PG16 and prior
 * because we gather slot information only for cluster versions greater than or
 * equal to PG17. See get_db_rel_and_slot_infos().
 */
int
count_old_cluster_logical_slots(void)
{
    int         slot_count = 0;
 
    for (int dbnum = 0; dbnum < old_cluster.dbarr.ndbs; dbnum++)
        slot_count += old_cluster.dbarr.dbs[dbnum].slot_arr.nslots;
 
    return slot_count;
}
 
/*
 * get_subscription_info()
 *
 * Gets the information of subscriptions in the cluster.
 */
void
get_subscription_info(ClusterInfo *cluster)
{
    PGconn     *conn;
    PGresult   *res;
    int         i_nsub;
    int         i_retain_dead_tuples;
 
    conn = connectToServer(cluster, "template1");
    if (GET_MAJOR_VERSION(cluster->major_version) >= 1900)
        res = executeQueryOrDie(conn, "SELECT count(*) AS nsub,"
                                "COUNT(CASE WHEN subretaindeadtuples THEN 1 END) > 0 AS retain_dead_tuples "
                                "FROM pg_catalog.pg_subscription");
    else
        res = executeQueryOrDie(conn, "SELECT count(*) AS nsub,"
                                "'f' AS retain_dead_tuples "
                                "FROM pg_catalog.pg_subscription");
 
    i_nsub = PQfnumber(res, "nsub");
    i_retain_dead_tuples = PQfnumber(res, "retain_dead_tuples");
 
    cluster->nsubs = atoi(PQgetvalue(res, 0, i_nsub));
    cluster->sub_retain_dead_tuples = (strcmp(PQgetvalue(res, 0, i_retain_dead_tuples), "t") == 0);
 
    PQclear(res);
    PQfinish(conn);
}
 
static void
free_db_and_rel_infos(DbInfoArr *db_arr)
{
    int         dbnum;
 
    for (dbnum = 0; dbnum < db_arr->ndbs; dbnum++)
    {
        free_rel_infos(&db_arr->dbs[dbnum].rel_arr);
        pg_free(db_arr->dbs[dbnum].db_name);
    }
    pg_free(db_arr->dbs);
    db_arr->dbs = NULL;
    db_arr->ndbs = 0;
}
 
 
static void
free_rel_infos(RelInfoArr *rel_arr)
{
    int         relnum;
 
    for (relnum = 0; relnum < rel_arr->nrels; relnum++)
    {
        if (rel_arr->rels[relnum].nsp_alloc)
            pg_free(rel_arr->rels[relnum].nspname);
        pg_free(rel_arr->rels[relnum].relname);
        if (rel_arr->rels[relnum].tblsp_alloc)
            pg_free(rel_arr->rels[relnum].tablespace);
    }
    pg_free(rel_arr->rels);
    rel_arr->nrels = 0;
}
 
 
static void
print_db_infos(DbInfoArr *db_arr)
{
    int         dbnum;
 
    for (dbnum = 0; dbnum < db_arr->ndbs; dbnum++)
    {
        DbInfo     *pDbInfo = &db_arr->dbs[dbnum];
 
        pg_log(PG_VERBOSE, "Database: \"%s\"", pDbInfo->db_name);
        print_rel_infos(&pDbInfo->rel_arr);
        print_slot_infos(&pDbInfo->slot_arr);
    }
}
 
 
static void
print_rel_infos(RelInfoArr *rel_arr)
{
    int         relnum;
 
    for (relnum = 0; relnum < rel_arr->nrels; relnum++)
        pg_log(PG_VERBOSE, "relname: \"%s.%s\", reloid: %u, reltblspace: \"%s\"",
               rel_arr->rels[relnum].nspname,
               rel_arr->rels[relnum].relname,
               rel_arr->rels[relnum].reloid,
               rel_arr->rels[relnum].tablespace);
}
 
static void
print_slot_infos(LogicalSlotInfoArr *slot_arr)
{
    /* Quick return if there are no logical slots. */
    if (slot_arr->nslots == 0)
        return;
 
    pg_log(PG_VERBOSE, "Logical replication slots in the database:");
 
    for (int slotnum = 0; slotnum < slot_arr->nslots; slotnum++)
    {
        LogicalSlotInfo *slot_info = &slot_arr->slots[slotnum];
 
        pg_log(PG_VERBOSE, "slot name: \"%s\", output plugin: \"%s\", two_phase: %s",
               slot_info->slotname,
               slot_info->plugin,
               slot_info->two_phase ? "true" : "false");
    }
}