datachecksum_state.c

Go to the documentation of this file.

/*-------------------------------------------------------------------------
 *
 * datachecksum_state.c
 *    Background worker for enabling or disabling data checksums online as
 *    well as functionality for manipulating data checksum state
 *
 * When enabling data checksums on a cluster at initdb time or when shut down
 * with pg_checksums, no extra process is required as each page is checksummed,
 * and verified, when accessed.  When enabling checksums on an already running
 * cluster, this worker will ensure that all pages are checksummed before
 * verification of the checksums is turned on. In the case of disabling
 * checksums, the state transition is performed only in the control file, no
 * changes are performed on the data pages.
 *
 * Checksums can be either enabled or disabled cluster-wide, with on/off being
 * the end state for data_checksums.
 *
 * 1. Enabling checksums
 * ---------------------
 * When enabling checksums in an online cluster, data_checksums will be set to
 * "inprogress-on" which signals that write operations MUST compute and write
 * the checksum on the data page, but during reading the checksum SHALL NOT be
 * verified. This ensures that all objects created while checksums are being
 * enabled will have checksums set, but reads won't fail due to missing or
 * invalid checksums. Invalid checksums can be present in case the cluster had
 * checksums enabled, then disabled them and updated the page while they were
 * disabled.
 *
 * The DataChecksumsWorker will compile a list of all databases at the start,
 * any databases created concurrently will see the in-progress state and will
 * be checksummed automatically.  All databases from the original list MUST BE
 * successfully processed in order for data checksums to be enabled, the only
 * exception are databases which are dropped before having been processed.
 *
 * For each database, all relations which have storage are read and every data
 * page is marked dirty to force a write with the checksum. This will generate
 * a lot of WAL as the entire database is read and written.
 *
 * If the processing is interrupted by a cluster crash or restart, it needs to
 * be restarted from the beginning again as state isn't persisted.
 *
 * 2. Disabling checksums
 * ----------------------
 * When disabling checksums, data_checksums will be set to "inprogress-off"
 * which signals that checksums are written but no longer need to be verified.
 * This ensures that backends which have not yet transitioned to the
 * "inprogress-off" state will still see valid checksums on pages.
 *
 * 3. Synchronization and Correctness
 * ----------------------------------
 * The processes involved in enabling or disabling data checksums in an
 * online cluster must be properly synchronized with the normal backends
 * serving concurrent queries to ensure correctness. Correctness is defined
 * as the following:
 *
 *    - Backends SHALL NOT violate the data_checksums state they have agreed to
 *      by acknowledging the procsignalbarrier:  This means that all backends
 *      MUST calculate and write data checksums during all states except off;
 *      MUST validate checksums only in the 'on' state.
 *    - Data checksums SHALL NOT be considered enabled cluster-wide until all
 *      currently connected backends have state "on": This means that all
 *      backends must wait on the procsignalbarrier to be acknowledged by all
 *      before proceeding to validate data checksums.
 *
 * There are two steps of synchronization required for changing data_checksums
 * in an online cluster: (i) changing state in the active backends ("on",
 * "off", "inprogress-on" and "inprogress-off"), and (ii) ensuring no
 * incompatible objects and processes are left in a database when workers end.
 * The former deals with cluster-wide agreement on data checksum state and the
 * latter with ensuring that any concurrent activity cannot break the data
 * checksum contract during processing.
 *
 * Synchronizing the state change is done with procsignal barriers. Before
 * updating the data_checksums state in the control file, all other backends must absorb the
 * barrier.  Barrier absorption will happen during interrupt processing, which
 * means that connected backends will change state at different times.  If
 * waiting for a barrier is done during startup, for example during replay, it
 * is important to realize that any locks held by the startup process might
 * cause deadlocks if backends end up waiting for those locks while startup
 * is waiting for a procsignalbarrier.
 *
 * 3.1 When Enabling Data Checksums
 * --------------------------------
 * A process which fails to observe data checksums being enabled can induce two
 * types of errors: failing to write the checksum when modifying the page and
 * failing to validate the data checksum on the page when reading it.
 *
 * When processing starts all backends belong to one of the below sets, with
 * one of Bd and Bi being empty:
 *
 * Bg: Backend updating the global state and emitting the procsignalbarrier
 * Bd: Backends in "off" state
 * Bi: Backends in "inprogress-on" state
 *
 * If processing is started in an online cluster then all backends are in Bd.
 * If processing was halted by the cluster shutting down (due to a crash or
 * intentional restart), the controlfile state "inprogress-on" will be observed
 * on system startup and all backends will be placed in Bd. The controlfile
 * state will also be set to "off".
 *
 * Backends transition Bd -> Bi via a procsignalbarrier which is emitted by the
 * DataChecksumsWorkerLauncherMain.  When all backends have acknowledged the
 * barrier then Bd will be empty and the next phase can begin: calculating and
 * writing data checksums with DataChecksumsWorkers.  When the
 * DataChecksumsWorker processes have finished writing checksums on all pages,
 * data checksums are enabled cluster-wide via another procsignalbarrier.
 * There are four sets of backends where Bd shall be an empty set:
 *
 * Bg: Backend updating the global state and emitting the procsignalbarrier
 * Bd: Backends in "off" state
 * Be: Backends in "on" state
 * Bi: Backends in "inprogress-on" state
 *
 * Backends in Bi and Be will write checksums when modifying a page, but only
 * backends in Be will verify the checksum during reading. The Bg backend is
 * blocked waiting for all backends in Bi to process interrupts and move to
 * Be. Any backend starting while Bg is waiting on the procsignalbarrier will
 * observe the global state being "on" and will thus automatically belong to
 * Be.  Checksums are enabled cluster-wide when Bi is an empty set. Bi and Be
 * are compatible sets while still operating based on their local state as
 * both write data checksums.
 *
 * 3.2 When Disabling Data Checksums
 * ---------------------------------
 * A process which fails to observe that data checksums have been disabled
 * can induce two types of errors: writing the checksum when modifying the
 * page and validating a data checksum which is no longer correct due to
 * modifications to the page. The former is not an error per se as data
 * integrity is maintained, but it is wasteful.  The latter will cause errors
 * in user operations.  Assuming the following sets of backends:
 *
 * Bg: Backend updating the global state and emitting the procsignalbarrier
 * Bd: Backends in "off" state
 * Be: Backends in "on" state
 * Bo: Backends in "inprogress-off" state
 * Bi: Backends in "inprogress-on" state
 *
 * Backends transition from the Be state to Bd like so: Be -> Bo -> Bd.  From
 * all other states, the transition can be straight to Bd.
 *
 * The goal is to transition all backends to Bd making the others empty sets.
 * Backends in Bo write data checksums, but don't validate them, such that
 * backends still in Be can continue to validate pages until the barrier has
 * been absorbed such that they are in Bo. Once all backends are in Bo, the
 * barrier to transition to "off" can be raised and all backends can safely
 * stop writing data checksums as no backend is enforcing data checksum
 * validation any longer.
 *
 * 4. Future opportunities for optimizations
 * -----------------------------------------
 * Below are some potential optimizations and improvements which were brought
 * up during reviews of this feature, but which weren't implemented in the
 * initial version. These are ideas listed without any validation on their
 * feasibility or potential payoff. More discussion on (most of) these can be
 * found on the -hackers threads linked to in the commit message of this
 * feature.
 *
 *   * Launching datachecksumsworker for resuming operation from the startup
 *     process: Currently users have to restart processing manually after a
 *     restart since dynamic background worker cannot be started from the
 *     postmaster. Changing the startup process could make restarting the
 *     processing automatic on cluster restart.
 *   * Avoid dirtying the page when checksums already match: Iff the checksum
 *     on the page happens to already match we still dirty the page. It should
 *     be enough to only do the log_newpage_buffer() call in that case.
 *   * Teach pg_checksums to avoid checksummed pages when pg_checksums is used
 *     to enable checksums on a cluster which is in inprogress-on state and
 *     may have checksummed pages (make pg_checksums be able to resume an
 *     online operation). This should only be attempted for wal_level minimal.
 *   * Restartability (not necessarily with page granularity).
 *   * Avoid processing databases which were created during inprogress-on.
 *     Right now all databases are processed regardless to be safe.
 *   * Teach CREATE DATABASE to calculate checksums for databases created
 *     during inprogress-on with a template database which has yet to be
 *     processed.
 *
 *
 * Portions Copyright (c) 1996-2026, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/postmaster/datachecksum_state.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"
 
#include "access/genam.h"
#include "access/heapam.h"
#include "access/htup_details.h"
#include "access/xact.h"
#include "access/xlog.h"
#include "access/xloginsert.h"
#include "catalog/indexing.h"
#include "catalog/pg_class.h"
#include "catalog/pg_database.h"
#include "commands/progress.h"
#include "commands/vacuum.h"
#include "common/relpath.h"
#include "miscadmin.h"
#include "pgstat.h"
#include "postmaster/bgworker.h"
#include "postmaster/bgwriter.h"
#include "postmaster/datachecksum_state.h"
#include "storage/bufmgr.h"
#include "storage/checksum.h"
#include "storage/ipc.h"
#include "storage/latch.h"
#include "storage/lmgr.h"
#include "storage/lwlock.h"
#include "storage/procarray.h"
#include "storage/smgr.h"
#include "storage/subsystems.h"
#include "tcop/tcopprot.h"
#include "utils/builtins.h"
#include "utils/fmgroids.h"
#include "utils/injection_point.h"
#include "utils/lsyscache.h"
#include "utils/ps_status.h"
#include "utils/syscache.h"
#include "utils/wait_event.h"
 
/*
 * Configuration of conditions which must match when absorbing a procsignal
 * barrier during data checksum enable/disable operations.  A single function
 * is used for absorbing all barriers, and the current and target states must
 * be defined as a from/to tuple in the checksum_barriers struct.
 */
typedef struct ChecksumBarrierCondition
{
    /* Current state of data checksums */
    int         from;
    /* Target state for data checksums */
    int         to;
} ChecksumBarrierCondition;
 
static const ChecksumBarrierCondition checksum_barriers[9] =
{
    /*
     * Disabling checksums: If checksums are currently enabled, disabling must
     * go through the 'inprogress-off' state.
     */
    {PG_DATA_CHECKSUM_VERSION, PG_DATA_CHECKSUM_INPROGRESS_OFF},
    {PG_DATA_CHECKSUM_INPROGRESS_OFF, PG_DATA_CHECKSUM_OFF},
 
    /*
     * If checksums are in the process of being enabled, but are not yet being
     * verified, we can abort by going back to 'off' state.
     */
    {PG_DATA_CHECKSUM_INPROGRESS_ON, PG_DATA_CHECKSUM_OFF},
 
    /*
     * Enabling checksums must normally go through the 'inprogress-on' state.
     */
    {PG_DATA_CHECKSUM_OFF, PG_DATA_CHECKSUM_INPROGRESS_ON},
    {PG_DATA_CHECKSUM_INPROGRESS_ON, PG_DATA_CHECKSUM_VERSION},
 
    /*
     * If checksums are being disabled but all backends are still computing
     * checksums, we can go straight back to 'on'
     */
    {PG_DATA_CHECKSUM_INPROGRESS_OFF, PG_DATA_CHECKSUM_VERSION},
 
    /*
     * If checksums are being enabled when launcher_exit is executed, state is
     * set to off since we cannot reach on at that point.
     */
    {PG_DATA_CHECKSUM_INPROGRESS_ON, PG_DATA_CHECKSUM_INPROGRESS_OFF},
 
    /*
     * Transitions that can happen when a new request is made while another is
     * currently being processed.
     */
    {PG_DATA_CHECKSUM_INPROGRESS_OFF, PG_DATA_CHECKSUM_INPROGRESS_ON},
    {PG_DATA_CHECKSUM_OFF, PG_DATA_CHECKSUM_INPROGRESS_OFF},
};
 
/* Possible operations the DataChecksumsWorker can perform */
typedef enum DataChecksumsWorkerOperation
{
    ENABLE_DATACHECKSUMS,
    DISABLE_DATACHECKSUMS,
} DataChecksumsWorkerOperation;
 
/* Possible states for a database entry which has been processed */
typedef enum
{
    DATACHECKSUMSWORKER_SUCCESSFUL = 0,
    DATACHECKSUMSWORKER_ABORTED,
    DATACHECKSUMSWORKER_FAILED,
    DATACHECKSUMSWORKER_DROPDB,
} DataChecksumsWorkerResult;
 
/*
 * Signaling between backends calling pg_enable/disable_data_checksums, the
 * checksums launcher process, and the checksums worker process.
 *
 * This struct is protected by DataChecksumsWorkerLock
 */
typedef struct DataChecksumsStateStruct
{
    /*
     * These are set by pg_{enable|disable}_data_checksums, to tell the
     * launcher what the target state is.
     */
    DataChecksumsWorkerOperation launch_operation;
    int         launch_cost_delay;
    int         launch_cost_limit;
 
    /*
     * Is a launcher process currently running?  This is set by the main
     * launcher process, after it has read the above launch_* parameters.
     */
    bool        launcher_running;
 
    /*
     * Every time a new worker is launched, it's assigned a unique invocation
     * number by incrementing this counter.
     */
    uint64      worker_invocation_counter;
 
    /*
     * Information about the current worker, if it's currently running.  These
     * are set by the worker launcher.
     */
    uint64      worker_invocation;  /* unique invocation number */
    Oid         database_oid;   /* database it's processing */
    pid_t       worker_pid;     /* worker process's PID */
 
    /*
     * These fields indicate the target state that the worker is currently
     * running with.  They can be different from the corresponding launch_*
     * fields, if a new pg_enable/disable_data_checksums() call was made while
     * the launcher/worker was already running.  The worker will periodically
     * check if new cost settings have been requested, and if so will copy
     * them from the launch_* fields and reset cost throttling to match the
     * new values.
     */
    DataChecksumsWorkerOperation operation;
    int         cost_delay;
    int         cost_limit;
 
    /*
     * Signaling between the launcher and the worker process. Protected by
     * DataChecksumsWorkerLock.
     */
 
    /* result, set by worker before exiting */
    DataChecksumsWorkerResult worker_result;
 
    /*
     * Tells the worker process whether it should also process the shared
     * catalogs
     */
    bool        process_shared_catalogs;
} DataChecksumsStateStruct;
 
/* Shared memory segment for datachecksumsworker */
static DataChecksumsStateStruct *DataChecksumState;
 
typedef struct DataChecksumsWorkerDatabase
{
    Oid         dboid;
    char       *dbname;
} DataChecksumsWorkerDatabase;
 
/* Flag set by the interrupt handler */
static volatile sig_atomic_t abort_requested = false;
 
static uint64 worker_invocation;
 
/*
 * Have we set the DataChecksumsStateStruct->launcher_running flag?
 * If we have, we need to clear it before exiting!
 */
static volatile sig_atomic_t launcher_running = false;
 
/* Are we enabling data checksums, or disabling them? */
static DataChecksumsWorkerOperation operation;
 
/* Prototypes */
static void StartDataChecksumsWorkerLauncher(DataChecksumsWorkerOperation op,
                                             int cost_delay,
                                             int cost_limit);
static void DataChecksumsShmemRequest(void *arg);
static bool DatabaseExists(Oid dboid);
static List *BuildDatabaseList(void);
static List *BuildRelationList(bool temp_relations, bool include_shared);
static void FreeDatabaseList(List *dblist);
static DataChecksumsWorkerResult ProcessDatabase(DataChecksumsWorkerDatabase *db);
static bool ProcessAllDatabases(void);
static bool ProcessSingleRelationFork(Relation reln, ForkNumber forkNum, BufferAccessStrategy strategy);
static void ResetDataChecksumsProgressCounters(void);
static void launcher_cancel_handler(SIGNAL_ARGS);
static void WaitForAllTransactionsToFinish(void);
 
const ShmemCallbacks DataChecksumsShmemCallbacks = {
    .request_fn = DataChecksumsShmemRequest,
};
 
#define CHECK_FOR_LAUNCHER_ABORT_REQUEST() \
    do {                                                            \
        Assert(MyBackendType == B_DATACHECKSUMSWORKER_LAUNCHER);    \
        LWLockAcquire(DataChecksumsWorkerLock, LW_SHARED);          \
        if (DataChecksumState->launch_operation != operation)       \
            abort_requested = true;                                 \
        LWLockRelease(DataChecksumsWorkerLock);                     \
    } while (0)
 
#define CHECK_FOR_WORKER_ABORT_REQUEST() \
    do {                                                            \
        Assert(MyBackendType == B_DATACHECKSUMSWORKER_WORKER);      \
        LWLockAcquire(DataChecksumsWorkerLock, LW_SHARED);          \
        if (DataChecksumState->worker_invocation != worker_invocation || \
            DataChecksumState->launch_operation != operation)       \
            abort_requested = true;                                 \
        LWLockRelease(DataChecksumsWorkerLock);                     \
    } while (0)
 
 
/*****************************************************************************
 * Functionality for manipulating the data checksum state in the cluster
 */
 
void
EmitAndWaitDataChecksumsBarrier(uint32 state)
{
    uint64      barrier;
 
    switch (state)
    {
        case PG_DATA_CHECKSUM_INPROGRESS_ON:
            barrier = EmitProcSignalBarrier(PROCSIGNAL_BARRIER_CHECKSUM_INPROGRESS_ON);
            WaitForProcSignalBarrier(barrier);
            break;
 
        case PG_DATA_CHECKSUM_INPROGRESS_OFF:
            barrier = EmitProcSignalBarrier(PROCSIGNAL_BARRIER_CHECKSUM_INPROGRESS_OFF);
            WaitForProcSignalBarrier(barrier);
            break;
 
        case PG_DATA_CHECKSUM_VERSION:
            barrier = EmitProcSignalBarrier(PROCSIGNAL_BARRIER_CHECKSUM_ON);
            WaitForProcSignalBarrier(barrier);
            break;
 
        case PG_DATA_CHECKSUM_OFF:
            barrier = EmitProcSignalBarrier(PROCSIGNAL_BARRIER_CHECKSUM_OFF);
            WaitForProcSignalBarrier(barrier);
            break;
 
        default:
            Assert(false);
    }
}
 
/*
 * AbsorbDataChecksumsBarrier
 *      Generic function for absorbing data checksum state changes
 *
 * All procsignalbarriers regarding data checksum state changes are absorbed
 * with this function.  The set of conditions required for the state change to
 * be accepted are listed in the checksum_barriers struct, target_state is
 * used to look up the relevant entry.
 */
bool
AbsorbDataChecksumsBarrier(ProcSignalBarrierType barrier)
{
    uint32      target_state;
    int         current = data_checksums;
    bool        found = false;
 
    /*
     * Translate the barrier condition to the target state, doing it here
     * instead of in the procsignal code saves the latter from knowing about
     * checksum states.
     */
    switch (barrier)
    {
        case PROCSIGNAL_BARRIER_CHECKSUM_INPROGRESS_ON:
            target_state = PG_DATA_CHECKSUM_INPROGRESS_ON;
            break;
        case PROCSIGNAL_BARRIER_CHECKSUM_ON:
            target_state = PG_DATA_CHECKSUM_VERSION;
            break;
        case PROCSIGNAL_BARRIER_CHECKSUM_INPROGRESS_OFF:
            target_state = PG_DATA_CHECKSUM_INPROGRESS_OFF;
            break;
        case PROCSIGNAL_BARRIER_CHECKSUM_OFF:
            target_state = PG_DATA_CHECKSUM_OFF;
            break;
        default:
            elog(ERROR, "incorrect barrier \"%i\" received", barrier);
    }
 
    /*
     * If the target state matches the current state then the barrier has been
     * repeated.
     */
    if (current == target_state)
        return true;
 
    /*
     * If the cluster is in recovery we skip the validation of current state
     * since the replay is trusted.
     */
    if (RecoveryInProgress())
    {
        SetLocalDataChecksumState(target_state);
        return true;
    }
 
    /*
     * Find the barrier condition definition for the target state. Not finding
     * a condition would be a grave programmer error as the states are a
     * discrete set.
     */
    for (size_t i = 0; i < lengthof(checksum_barriers) && !found; i++)
    {
        if (checksum_barriers[i].from == current && checksum_barriers[i].to == target_state)
            found = true;
    }
 
    /*
     * If the relevant state criteria aren't satisfied, throw an error which
     * will be caught by the procsignal machinery for a later retry.
     */
    if (!found)
        ereport(ERROR,
                errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                errmsg("incorrect data checksum state %i for target state %i",
                       current, target_state));
 
    SetLocalDataChecksumState(target_state);
    return true;
}
 
 
/*
 * Disables data checksums for the cluster, if applicable. Starts a background
 * worker which turns off the data checksums.
 */
Datum
disable_data_checksums(PG_FUNCTION_ARGS)
{
    PreventCommandDuringRecovery("pg_disable_data_checksums()");
 
    if (!superuser())
        ereport(ERROR,
                errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                errmsg("must be superuser to change data checksum state"));
 
    StartDataChecksumsWorkerLauncher(DISABLE_DATACHECKSUMS, 0, 0);
    PG_RETURN_VOID();
}
 
/*
 * Enables data checksums for the cluster, if applicable.  Supports vacuum-
 * like cost based throttling to limit system load. Starts a background worker
 * which updates data checksums on existing data.
 */
Datum
enable_data_checksums(PG_FUNCTION_ARGS)
{
    int         cost_delay = PG_GETARG_INT32(0);
    int         cost_limit = PG_GETARG_INT32(1);
 
    PreventCommandDuringRecovery("pg_enable_data_checksums()");
 
    if (!superuser())
        ereport(ERROR,
                errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                errmsg("must be superuser to change data checksum state"));
 
    if (cost_delay < 0)
        ereport(ERROR,
                errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                errmsg("cost delay cannot be a negative value"));
 
    if (cost_limit <= 0)
        ereport(ERROR,
                errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                errmsg("cost limit must be greater than zero"));
 
    StartDataChecksumsWorkerLauncher(ENABLE_DATACHECKSUMS, cost_delay, cost_limit);
 
    PG_RETURN_VOID();
}
 
 
/*****************************************************************************
 * Functionality for running the datachecksumsworker and associated launcher
 */
 
/*
 * StartDataChecksumsWorkerLauncher
 *      Start the datachecksumsworker launcher process, if not running yet
 *
 * This is called to start data checksums processing for enabling as well as
 * disabling.
 */
static void
StartDataChecksumsWorkerLauncher(DataChecksumsWorkerOperation op,
                                 int cost_delay,
                                 int cost_limit)
{
    BackgroundWorker bgw;
    BackgroundWorkerHandle *bgw_handle;
    bool        running;
 
#ifdef USE_ASSERT_CHECKING
    /* The cost delay settings have no effect when disabling */
    if (op == DISABLE_DATACHECKSUMS)
        Assert(cost_delay == 0 && cost_limit == 0);
#endif
 
    INJECTION_POINT("datachecksumsworker-startup-delay", NULL);
 
    /* Store the desired state in shared memory */
    LWLockAcquire(DataChecksumsWorkerLock, LW_EXCLUSIVE);
 
    DataChecksumState->launch_operation = op;
    DataChecksumState->launch_cost_delay = cost_delay;
    DataChecksumState->launch_cost_limit = cost_limit;
 
    /* Is the launcher already running? If so, what is it doing? */
    running = DataChecksumState->launcher_running;
 
    LWLockRelease(DataChecksumsWorkerLock);
 
    /*
     * Launch a new launcher process, if it's not running already.
     *
     * If the launcher is currently busy enabling the checksums, and we want
     * them disabled (or vice versa), the launcher will notice that at latest
     * when it's about to exit, and will loop back to process the new request.
     * So if the launcher is already running, we don't need to do anything
     * more here to abort it.
     *
     * If you call pg_enable/disable_data_checksums() twice in a row, before
     * the launcher has had a chance to start up, we still end up launching it
     * twice.  That's OK, the second invocation will see that a launcher is
     * already running and exit quickly.
     */
    if (!running)
    {
        if ((op == ENABLE_DATACHECKSUMS && DataChecksumsOn()) ||
            (op == DISABLE_DATACHECKSUMS && DataChecksumsOff()))
        {
            ereport(LOG,
                    errmsg("data checksums already in desired state, exiting"));
            return;
        }
 
        /*
         * Prepare the BackgroundWorker and launch it.
         */
        memset(&bgw, 0, sizeof(bgw));
        bgw.bgw_flags = BGWORKER_SHMEM_ACCESS | BGWORKER_BACKEND_DATABASE_CONNECTION;
        bgw.bgw_start_time = BgWorkerStart_RecoveryFinished;
        snprintf(bgw.bgw_library_name, BGW_MAXLEN, "postgres");
        snprintf(bgw.bgw_function_name, BGW_MAXLEN, "DataChecksumsWorkerLauncherMain");
        snprintf(bgw.bgw_name, BGW_MAXLEN, "datachecksums launcher");
        snprintf(bgw.bgw_type, BGW_MAXLEN, "datachecksums launcher");
        bgw.bgw_restart_time = BGW_NEVER_RESTART;
        bgw.bgw_notify_pid = MyProcPid;
        bgw.bgw_main_arg = (Datum) 0;
 
        if (!RegisterDynamicBackgroundWorker(&bgw, &bgw_handle))
            ereport(ERROR,
                    errcode(ERRCODE_INSUFFICIENT_RESOURCES),
                    errmsg("failed to start background worker to process data checksums"));
    }
    else
    {
        ereport(LOG,
                errmsg("data checksum processing already running"));
    }
}
 
/*
 * ProcessSingleRelationFork
 *      Enable data checksums in a single relation/fork.
 *
 * Returns true if successful, and false if *aborted*. On error, an actual
 * error is raised in the lower levels.
 */
static bool
ProcessSingleRelationFork(Relation reln, ForkNumber forkNum, BufferAccessStrategy strategy)
{
    BlockNumber numblocks = RelationGetNumberOfBlocksInFork(reln, forkNum);
    char        activity[NAMEDATALEN * 2 + 128];
    char       *relns;
 
    relns = get_namespace_name(RelationGetNamespace(reln));
 
    /* Report the current relation to pg_stat_activity */
    snprintf(activity, sizeof(activity) - 1, "processing: %s.%s (%s, %u blocks)",
             (relns ? relns : ""), RelationGetRelationName(reln), forkNames[forkNum], numblocks);
    pgstat_report_activity(STATE_RUNNING, activity);
    {
        const int   index[] = {
            PROGRESS_DATACHECKSUMS_BLOCKS_TOTAL,
            PROGRESS_DATACHECKSUMS_BLOCKS_DONE
        };
 
        int64       vals[2];
 
        vals[0] = numblocks;
        vals[1] = 0;
 
        pgstat_progress_update_multi_param(2, index, vals);
    }
    if (relns)
        pfree(relns);
 
    /*
     * We are looping over the blocks which existed at the time of process
     * start, which is safe since new blocks are created with checksums set
     * already due to the state being "inprogress-on".
     */
    for (BlockNumber blknum = 0; blknum < numblocks; blknum++)
    {
        Buffer      buf = ReadBufferExtended(reln, forkNum, blknum, RBM_NORMAL, strategy);
 
        /* Need to get an exclusive lock to mark the buffer as dirty */
        LockBuffer(buf, BUFFER_LOCK_EXCLUSIVE);
 
        /*
         * Mark the buffer as dirty and force a full page write.  We have to
         * re-write the page to WAL even if the checksum hasn't changed,
         * because if there is a replica it might have a slightly different
         * version of the page with an invalid checksum, caused by unlogged
         * changes (e.g. hint bits) on the primary happening while checksums
         * were off. This can happen if there was a valid checksum on the page
         * at one point in the past, so only when checksums are first on, then
         * off, and then turned on again.  TODO: investigate if this could be
         * avoided if the checksum is calculated to be correct and wal_level
         * is set to "minimal".
         *
         * Unlogged relations don't need WAL since they are reset to their
         * init fork on recovery.  We still dirty the buffer so that the
         * checksum is written to disk at the next checkpoint.
         *
         * The init fork is an exception: it is WAL-logged so the standby can
         * materialize the relation after promotion (see
         * ResetUnloggedRelations()).  Skipping it here would leave the
         * standby with a stale init fork that, once copied to the main fork
         * on promotion, would fail checksum verification on every read.
         */
        START_CRIT_SECTION();
        MarkBufferDirty(buf);
        if (RelationNeedsWAL(reln) || forkNum == INIT_FORKNUM)
            log_newpage_buffer(buf, false);
        END_CRIT_SECTION();
 
        UnlockReleaseBuffer(buf);
 
        /* Check if we are asked to abort, the abortion will bubble up. */
        Assert(operation == ENABLE_DATACHECKSUMS);
        CHECK_FOR_WORKER_ABORT_REQUEST();
        if (abort_requested)
            return false;
 
        /* update the block counter */
        pgstat_progress_update_param(PROGRESS_DATACHECKSUMS_BLOCKS_DONE,
                                     (blknum + 1));
 
        /*
         * Processing is re-using the vacuum cost delay for process
         * throttling, hence why we call vacuum APIs here.
         */
        vacuum_delay_point(false);
    }
 
    return true;
}
 
/*
 * Initialize all data checksum progress counters to be displayed as NULL.
 */
static void
ResetDataChecksumsProgressCounters(void)
{
    const int   index[] = {
        PROGRESS_DATACHECKSUMS_DBS_TOTAL,
        PROGRESS_DATACHECKSUMS_DBS_DONE,
        PROGRESS_DATACHECKSUMS_RELS_TOTAL,
        PROGRESS_DATACHECKSUMS_RELS_DONE,
        PROGRESS_DATACHECKSUMS_BLOCKS_TOTAL,
        PROGRESS_DATACHECKSUMS_BLOCKS_DONE,
    };
 
    int64       vals[lengthof(index)];
 
    for (size_t i = 0; i < lengthof(index); i++)
        vals[i] = -1;
 
    pgstat_progress_update_multi_param(lengthof(index), index, vals);
}
 
/*
 * ProcessSingleRelationByOid
 *      Process a single relation based on oid.
 *
 * Returns true if successful, and false if *aborted*. On error, an actual
 * error is raised in the lower levels.
 */
static bool
ProcessSingleRelationByOid(Oid relationId, BufferAccessStrategy strategy)
{
    Relation    rel;
    bool        aborted = false;
 
    StartTransactionCommand();
 
    rel = try_relation_open(relationId, AccessShareLock);
    if (rel == NULL)
    {
        /*
         * Relation no longer exists. We don't consider this an error since
         * there are no pages in it that need data checksums, and thus return
         * true. The worker operates off a list of relations generated at the
         * start of processing, so relations being dropped in the meantime is
         * to be expected.
         */
        CommitTransactionCommand();
        pgstat_report_activity(STATE_IDLE, NULL);
        return true;
    }
    RelationGetSmgr(rel);
 
    for (ForkNumber fnum = 0; fnum <= MAX_FORKNUM; fnum++)
    {
        if (smgrexists(rel->rd_smgr, fnum))
        {
            if (!ProcessSingleRelationFork(rel, fnum, strategy))
            {
                aborted = true;
                break;
            }
        }
    }
    relation_close(rel, AccessShareLock);
 
    CommitTransactionCommand();
    pgstat_report_activity(STATE_IDLE, NULL);
 
    return !aborted;
}
 
/*
 * ProcessDatabase
 *      Enable data checksums in a single database.
 *
 * We do this by launching a dynamic background worker into this database, and
 * waiting for it to finish.  We have to do this in a separate worker, since
 * each process can only be connected to one database during its lifetime.
 */
static DataChecksumsWorkerResult
ProcessDatabase(DataChecksumsWorkerDatabase *db)
{
    BackgroundWorker bgw;
    BackgroundWorkerHandle *bgw_handle;
    BgwHandleStatus status;
    pid_t       pid;
    uint64      invocation;
    char        activity[NAMEDATALEN + 64];
    DataChecksumsWorkerResult result;
 
    LWLockAcquire(DataChecksumsWorkerLock, LW_EXCLUSIVE);
 
    /*
     * Initialize result to FAILED.  The worker will change it to SUCCESSFUL
     * if it completes successfully.
     */
    DataChecksumState->worker_result = DATACHECKSUMSWORKER_FAILED;
    DataChecksumState->worker_pid = InvalidPid;
 
    invocation = ++DataChecksumState->worker_invocation_counter;
    DataChecksumState->worker_invocation = invocation;
    DataChecksumState->database_oid = db->dboid;
 
    LWLockRelease(DataChecksumsWorkerLock);
 
    memset(&bgw, 0, sizeof(bgw));
    bgw.bgw_flags = BGWORKER_SHMEM_ACCESS | BGWORKER_BACKEND_DATABASE_CONNECTION;
    bgw.bgw_start_time = BgWorkerStart_RecoveryFinished;
    snprintf(bgw.bgw_library_name, BGW_MAXLEN, "postgres");
    snprintf(bgw.bgw_function_name, BGW_MAXLEN, "%s", "DataChecksumsWorkerMain");
    snprintf(bgw.bgw_name, BGW_MAXLEN, "datachecksums worker");
    snprintf(bgw.bgw_type, BGW_MAXLEN, "datachecksums worker");
    bgw.bgw_restart_time = BGW_NEVER_RESTART;
    bgw.bgw_notify_pid = MyProcPid;
    /* pass the invocation number to the worker process */
    bgw.bgw_main_arg = UInt64GetDatum(invocation);
 
    /*
     * If there are no worker slots available, there is little we can do.  If
     * we retry in a bit it's still unlikely that the user has managed to
     * reconfigure in the meantime and we'd be run through retries fast.
     */
    if (!RegisterDynamicBackgroundWorker(&bgw, &bgw_handle))
    {
        ereport(WARNING,
                errmsg("could not start background worker for enabling data checksums in database \"%s\"",
                       db->dbname),
                errhint("The \"%s\" setting might be too low.", "max_worker_processes"));
        return DATACHECKSUMSWORKER_FAILED;
    }
 
    status = WaitForBackgroundWorkerStartup(bgw_handle, &pid);
    if (status == BGWH_STOPPED)
    {
        /*
         * If the worker managed to start, and stop, before we got to waiting
         * for it we can see a STOPPED status here without it being a failure.
         */
        LWLockAcquire(DataChecksumsWorkerLock, LW_SHARED);
        Assert(DataChecksumState->worker_invocation == invocation);
        if (DataChecksumState->worker_result == DATACHECKSUMSWORKER_SUCCESSFUL)
        {
            LWLockRelease(DataChecksumsWorkerLock);
            pgstat_report_activity(STATE_IDLE, NULL);
            return DATACHECKSUMSWORKER_SUCCESSFUL;
        }
        LWLockRelease(DataChecksumsWorkerLock);
 
        ereport(WARNING,
                errmsg("could not start background worker for enabling data checksums in database \"%s\"",
                       db->dbname),
                errhint("More details on the error might be found in the server log."));
 
        /*
         * Heuristic to see if the database was dropped, and if it was we can
         * treat it as not an error, else treat as fatal and error out.
         */
        if (DatabaseExists(db->dboid))
            return DATACHECKSUMSWORKER_FAILED;
        else
            return DATACHECKSUMSWORKER_DROPDB;
    }
 
    /*
     * If the postmaster crashed we cannot end up with a processed database so
     * we have no alternative other than exiting. When enabling checksums we
     * won't at this time have changed the data checksums state in pg_control
     * to enabled so when the cluster comes back up processing will have to be
     * restarted.
     */
    if (status == BGWH_POSTMASTER_DIED)
        ereport(FATAL,
                errcode(ERRCODE_ADMIN_SHUTDOWN),
                errmsg("cannot enable data checksums without the postmaster process"),
                errhint("Restart the database and restart data checksum processing by calling pg_enable_data_checksums()."));
 
    Assert(status == BGWH_STARTED);
    ereport(LOG,
            errmsg("initiating data checksum processing in database \"%s\"",
                   db->dbname));
 
    /* Save the pid of the worker so we can signal it later */
    LWLockAcquire(DataChecksumsWorkerLock, LW_EXCLUSIVE);
    Assert(DataChecksumState->worker_invocation == invocation);
    DataChecksumState->worker_pid = pid;
    LWLockRelease(DataChecksumsWorkerLock);
 
    snprintf(activity, sizeof(activity) - 1,
             "Waiting for worker in database %s (pid %ld)", db->dbname, (long) pid);
    pgstat_report_activity(STATE_RUNNING, activity);
 
    status = WaitForBackgroundWorkerShutdown(bgw_handle);
    if (status == BGWH_POSTMASTER_DIED)
        ereport(FATAL,
                errcode(ERRCODE_ADMIN_SHUTDOWN),
                errmsg("postmaster exited during data checksum processing in \"%s\"",
                       db->dbname),
                errhint("Restart the database and restart data checksum processing by calling pg_enable_data_checksums()."));
 
    LWLockAcquire(DataChecksumsWorkerLock, LW_EXCLUSIVE);
    Assert(DataChecksumState->worker_invocation == invocation);
    result = DataChecksumState->worker_result;
    DataChecksumState->worker_pid = InvalidPid;
    LWLockRelease(DataChecksumsWorkerLock);
 
    if (result == DATACHECKSUMSWORKER_ABORTED)
        ereport(LOG,
                errmsg("data checksums processing was aborted in database \"%s\"",
                       db->dbname));
    pgstat_report_activity(STATE_IDLE, NULL);
    return result;
}
 
/*
 * launcher_exit
 *
 * Internal routine for cleaning up state when a launcher process which has
 * performed checksum operations exits. A launcher process which is exiting due
 * to a duplicate started launcher does not need to perform any cleanup and
 * this function should not be called. Otherwise, we need to clean up the abort
 * flag to ensure that processing can be started again if it was previously
 * aborted (note: started again, *not* restarted from where it left off).
 */
static void
launcher_exit(int code, Datum arg)
{
    abort_requested = false;
 
    if (launcher_running)
    {
        LWLockAcquire(DataChecksumsWorkerLock, LW_EXCLUSIVE);
        if (DataChecksumState->worker_pid != InvalidPid)
        {
            ereport(LOG,
                    errmsg("data checksums launcher exiting while worker is still running, signalling worker"));
            kill(DataChecksumState->worker_pid, SIGTERM);
            DataChecksumState->worker_pid = InvalidPid;
        }
        LWLockRelease(DataChecksumsWorkerLock);
    }
 
    /*
     * If the launcher is exiting before data checksums are enabled then set
     * the state to off since processing cannot be resumed.
     */
    if (DataChecksumsInProgressOn())
        SetDataChecksumsOff();
 
    LWLockAcquire(DataChecksumsWorkerLock, LW_EXCLUSIVE);
    launcher_running = false;
    DataChecksumState->launcher_running = false;
    LWLockRelease(DataChecksumsWorkerLock);
}
 
/*
 * launcher_cancel_handler
 *
 * Internal routine for reacting to SIGINT and flagging the worker to abort.
 * The worker won't be interrupted immediately but will check for abort flag
 * between each block in a relation.
 */
static void
launcher_cancel_handler(SIGNAL_ARGS)
{
    int         save_errno = errno;
 
    abort_requested = true;
 
    /*
     * There is no sleeping in the main loop, the flag will be checked
     * periodically in ProcessSingleRelationFork. The worker does however
     * sleep when waiting for concurrent transactions to end so we still need
     * to set the latch.
     */
    SetLatch(MyLatch);
 
    errno = save_errno;
}
 
/*
 * WaitForAllTransactionsToFinish
 *      Blocks awaiting all current transactions to finish
 *
 * Returns when all transactions which are active at the call of the function
 * have ended.
 *
 * NB: this will return early, if aborted by SIGINT or if the target state
 * is changed while we're running.
 */
static void
WaitForAllTransactionsToFinish(void)
{
    TransactionId waitforxid;
 
    LWLockAcquire(XidGenLock, LW_SHARED);
    waitforxid = XidFromFullTransactionId(TransamVariables->nextXid);
    LWLockRelease(XidGenLock);
 
    while (TransactionIdPrecedes(GetOldestActiveTransactionId(false, true), waitforxid))
    {
        char        activity[64];
        int         rc;
 
        /* Oldest running xid is older than us, so wait */
        snprintf(activity,
                 sizeof(activity),
                 "Waiting for transactions older than %u to end",
                 waitforxid);
        pgstat_report_activity(STATE_RUNNING, activity);
 
        /* Retry every 3 seconds */
        ResetLatch(MyLatch);
        rc = WaitLatch(MyLatch,
                       WL_LATCH_SET | WL_TIMEOUT | WL_POSTMASTER_DEATH,
                       3000,
                       WAIT_EVENT_CHECKSUM_ENABLE_STARTCONDITION);
 
        /*
         * If the postmaster died, bail out.  But first print a log message to
         * note that the checksumming didn't complete.
         */
        if (rc & WL_POSTMASTER_DEATH)
            ereport(FATAL,
                    errcode(ERRCODE_ADMIN_SHUTDOWN),
                    errmsg("postmaster exited during data checksums processing"),
                    errhint("Data checksums processing must be restarted manually after cluster restart."));
 
        CHECK_FOR_INTERRUPTS();
        CHECK_FOR_LAUNCHER_ABORT_REQUEST();
 
        if (abort_requested)
            break;
    }
 
    pgstat_report_activity(STATE_IDLE, NULL);
    return;
}
 
/*
 * DataChecksumsWorkerLauncherMain
 *
 * Main function for launching dynamic background workers for processing data
 * checksums in databases. This function has the bgworker management, with
 * ProcessAllDatabases being responsible for looping over the databases and
 * initiating processing.
 */
void
DataChecksumsWorkerLauncherMain(Datum arg)
{
 
    ereport(DEBUG1,
            errmsg("background worker \"datachecksums launcher\" started"));
 
    pqsignal(SIGTERM, die);
    pqsignal(SIGINT, launcher_cancel_handler);
    pqsignal(SIGUSR1, procsignal_sigusr1_handler);
    pqsignal(SIGUSR2, PG_SIG_IGN);
 
    BackgroundWorkerUnblockSignals();
 
    MyBackendType = B_DATACHECKSUMSWORKER_LAUNCHER;
    init_ps_display(NULL);
 
    INJECTION_POINT("datachecksumsworker-launcher-delay", NULL);
 
    LWLockAcquire(DataChecksumsWorkerLock, LW_EXCLUSIVE);
 
    if (DataChecksumState->launcher_running)
    {
        ereport(LOG,
                errmsg("background worker \"datachecksums launcher\" already running, exiting"));
        /* Launcher was already running, let it finish */
        LWLockRelease(DataChecksumsWorkerLock);
        return;
    }
 
    on_shmem_exit(launcher_exit, 0);
    launcher_running = true;
 
    /* Initialize a connection to shared catalogs only */
    BackgroundWorkerInitializeConnectionByOid(InvalidOid, InvalidOid, 0);
 
    operation = DataChecksumState->launch_operation;
    DataChecksumState->launcher_running = true;
    DataChecksumState->operation = operation;
    DataChecksumState->cost_delay = DataChecksumState->launch_cost_delay;
    DataChecksumState->cost_limit = DataChecksumState->launch_cost_limit;
    LWLockRelease(DataChecksumsWorkerLock);
 
    /*
     * The target state can change while we are busy enabling/disabling
     * checksums, if the user calls pg_disable/enable_data_checksums() before
     * we are finished with the previous request. In that case, we will loop
     * back here, to process the new request.
     */
again:
 
    pgstat_progress_start_command(PROGRESS_COMMAND_DATACHECKSUMS,
                                  InvalidOid);
    ResetDataChecksumsProgressCounters();
 
    if (operation == ENABLE_DATACHECKSUMS)
    {
        /*
         * If we are asked to enable checksums in a cluster which already has
         * checksums enabled, exit immediately as there is nothing more to do.
         */
        if (DataChecksumsNeedVerify())
            goto done;
 
        ereport(LOG,
                errmsg("enabling data checksums requested, starting data checksum calculation"));
 
        /*
         * Set the state to inprogress-on and wait on the procsignal barrier.
         */
        pgstat_progress_update_param(PROGRESS_DATACHECKSUMS_PHASE,
                                     PROGRESS_DATACHECKSUMS_PHASE_ENABLING);
        SetDataChecksumsOnInProgress();
 
        /*
         * All backends are now in inprogress-on state and are writing data
         * checksums.  Start processing all data at rest.
         */
        if (!ProcessAllDatabases())
        {
            /*
             * If the target state changed during processing then it's not a
             * failure, so restart processing instead.
             */
            CHECK_FOR_LAUNCHER_ABORT_REQUEST();
            if (abort_requested)
                goto done;
            ereport(ERROR,
                    errcode(ERRCODE_INSUFFICIENT_RESOURCES),
                    errmsg("unable to enable data checksums in cluster"));
        }
 
        /*
         * Data checksums have been set on all pages, set the state to on in
         * order to instruct backends to validate checksums on reading.
         */
        SetDataChecksumsOn();
 
        ereport(LOG,
                errmsg("data checksums are now enabled"));
    }
    else if (operation == DISABLE_DATACHECKSUMS)
    {
        ereport(LOG,
                errmsg("disabling data checksums requested"));
 
        pgstat_progress_update_param(PROGRESS_DATACHECKSUMS_PHASE,
                                     PROGRESS_DATACHECKSUMS_PHASE_DISABLING);
        SetDataChecksumsOff();
        ereport(LOG,
                errmsg("data checksums are now disabled"));
    }
    else
        Assert(false);
 
done:
 
    /*
     * This state will only be displayed for a fleeting moment, but for the
     * sake of correctness it is still added before ending the command.
     */
    pgstat_progress_update_param(PROGRESS_DATACHECKSUMS_PHASE,
                                 PROGRESS_DATACHECKSUMS_PHASE_DONE);
 
    /*
     * All done. But before we exit, check if the target state was changed
     * while we were running. In that case we will have to start all over
     * again.
     */
    LWLockAcquire(DataChecksumsWorkerLock, LW_EXCLUSIVE);
    if (DataChecksumState->launch_operation != operation)
    {
        DataChecksumState->operation = DataChecksumState->launch_operation;
        operation = DataChecksumState->launch_operation;
        DataChecksumState->cost_delay = DataChecksumState->launch_cost_delay;
        DataChecksumState->cost_limit = DataChecksumState->launch_cost_limit;
        LWLockRelease(DataChecksumsWorkerLock);
        goto again;
    }
 
    /* Shut down progress reporting as we are done */
    pgstat_progress_end_command();
 
    launcher_running = false;
    DataChecksumState->launcher_running = false;
    LWLockRelease(DataChecksumsWorkerLock);
}
 
/*
 * ProcessAllDatabases
 *      Compute the list of all databases and process checksums in each
 *
 * This will generate a list of databases to process for enabling checksums.
 * If a database encounters a failure then processing will end immediately and
 * return an error.
 */
static bool
ProcessAllDatabases(void)
{
    List       *DatabaseList;
    int         cumulative_total = 0;
 
    /* Set up so first run processes shared catalogs, not once in every db */
    LWLockAcquire(DataChecksumsWorkerLock, LW_EXCLUSIVE);
    DataChecksumState->process_shared_catalogs = true;
    LWLockRelease(DataChecksumsWorkerLock);
 
    /* Get a list of all databases to process */
    WaitForAllTransactionsToFinish();
    DatabaseList = BuildDatabaseList();
 
    /*
     * Update progress reporting with the total number of databases we need to
     * process.  This number should not be changed during processing, the
     * columns for processed databases is instead increased such that it can
     * be compared against the total.
     */
    {
        const int   index[] = {
            PROGRESS_DATACHECKSUMS_DBS_TOTAL,
            PROGRESS_DATACHECKSUMS_DBS_DONE,
        };
 
        int64       vals[2];
 
        vals[0] = list_length(DatabaseList);
        vals[1] = 0;
 
        pgstat_progress_update_multi_param(2, index, vals);
    }
 
    foreach_ptr(DataChecksumsWorkerDatabase, db, DatabaseList)
    {
        DataChecksumsWorkerResult result;
 
        result = ProcessDatabase(db);
 
#ifdef USE_INJECTION_POINTS
        /* Allow a test process to alter the result of the operation */
        if (IS_INJECTION_POINT_ATTACHED("datachecksumsworker-fail-db-result"))
        {
            result = DATACHECKSUMSWORKER_FAILED;
            INJECTION_POINT_CACHED("datachecksumsworker-fail-db-result",
                                   db->dbname);
        }
#endif
 
        pgstat_progress_update_param(PROGRESS_DATACHECKSUMS_DBS_DONE,
                                     ++cumulative_total);
 
        if (result == DATACHECKSUMSWORKER_FAILED)
        {
            /*
             * Disable checksums on cluster, because we failed one of the
             * databases and this is an all or nothing process.
             */
            SetDataChecksumsOff();
            ereport(ERROR,
                    errcode(ERRCODE_INSUFFICIENT_RESOURCES),
                    errmsg("data checksums failed to get enabled in all databases, aborting"),
                    errhint("The server log might have more information on the cause of the error."));
        }
        else if (result == DATACHECKSUMSWORKER_ABORTED || abort_requested)
        {
            /* Abort flag set, so exit the whole process */
            return false;
        }
        else if (result == DATACHECKSUMSWORKER_DROPDB)
        {
            /*
             * Ignore databases that were dropped before their worker could
             * process them, and continue with the remaining databases.
             */
            continue;
        }
 
        /*
         * When one database has completed, it will have done shared catalogs
         * so we don't have to process them again.
         */
        LWLockAcquire(DataChecksumsWorkerLock, LW_EXCLUSIVE);
        DataChecksumState->process_shared_catalogs = false;
        LWLockRelease(DataChecksumsWorkerLock);
    }
 
    FreeDatabaseList(DatabaseList);
 
    pgstat_progress_update_param(PROGRESS_DATACHECKSUMS_PHASE,
                                 PROGRESS_DATACHECKSUMS_PHASE_WAITING_BARRIER);
    return true;
}
 
/*
 * DataChecksumsShmemRequest
 *      Request datachecksumsworker-related shared memory
 */
static void
DataChecksumsShmemRequest(void *arg)
{
    ShmemRequestStruct(.name = "DataChecksumsWorker Data",
                       .size = sizeof(DataChecksumsStateStruct),
                       .ptr = (void **) &DataChecksumState,
        );
}
 
/*
 * DatabaseExists
 *
 * Scans the system catalog to check if a database with the given Oid exists
 * and returns true if it is found and valid, else false. Note, we cannot use
 * database_is_invalid_oid here as it will ERROR out, and we want to gracefully
 * handle errors.
 */
static bool
DatabaseExists(Oid dboid)
{
    Relation    rel;
    ScanKeyData skey;
    SysScanDesc scan;
    bool        found;
    HeapTuple   tuple;
    Form_pg_database pg_database_tuple;
 
    StartTransactionCommand();
 
    rel = table_open(DatabaseRelationId, AccessShareLock);
    ScanKeyInit(&skey,
                Anum_pg_database_oid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(dboid));
    scan = systable_beginscan(rel, DatabaseOidIndexId, true, SnapshotSelf,
                              1, &skey);
    tuple = systable_getnext(scan);
    found = HeapTupleIsValid(tuple);
 
    /* If the Oid exists, ensure that it's not partially dropped */
    if (found)
    {
        pg_database_tuple = (Form_pg_database) GETSTRUCT(tuple);
        if (database_is_invalid_form(pg_database_tuple))
            found = false;
    }
 
    systable_endscan(scan);
    table_close(rel, AccessShareLock);
 
    CommitTransactionCommand();
 
    return found;
}
 
/*
 * BuildDatabaseList
 *      Compile a list of all currently available databases in the cluster
 *
 * This creates the list of databases for the datachecksumsworker workers to
 * add checksums to. If the caller wants to ensure that no concurrently
 * running CREATE DATABASE calls exist, this needs to be preceded by a call
 * to WaitForAllTransactionsToFinish().
 */
static List *
BuildDatabaseList(void)
{
    List       *DatabaseList = NIL;
    Relation    rel;
    TableScanDesc scan;
    HeapTuple   tup;
    MemoryContext ctx = CurrentMemoryContext;
    MemoryContext oldctx;
 
    StartTransactionCommand();
 
    rel = table_open(DatabaseRelationId, AccessShareLock);
    scan = table_beginscan_catalog(rel, 0, NULL);
 
    while (HeapTupleIsValid(tup = heap_getnext(scan, ForwardScanDirection)))
    {
        Form_pg_database pgdb = (Form_pg_database) GETSTRUCT(tup);
        DataChecksumsWorkerDatabase *db;
 
        oldctx = MemoryContextSwitchTo(ctx);
 
        db = (DataChecksumsWorkerDatabase *) palloc0(sizeof(DataChecksumsWorkerDatabase));
 
        db->dboid = pgdb->oid;
        db->dbname = pstrdup(NameStr(pgdb->datname));
 
        DatabaseList = lappend(DatabaseList, db);
 
        MemoryContextSwitchTo(oldctx);
    }
 
    table_endscan(scan);
    table_close(rel, AccessShareLock);
 
    CommitTransactionCommand();
 
    return DatabaseList;
}
 
static void
FreeDatabaseList(List *dblist)
{
    if (!dblist)
        return;
 
    foreach_ptr(DataChecksumsWorkerDatabase, db, dblist)
    {
        if (db->dbname != NULL)
            pfree(db->dbname);
    }
 
    list_free_deep(dblist);
}
 
/*
 * BuildRelationList
 *      Compile a list of relations in the database
 *
 * Returns a list of OIDs for the requested relation types. If temp_relations
 * is True then only temporary relations with storage are returned.  If
 * temp_relations is False then non-temporary relations with storage are
 * returned.  If include_shared is True then shared relations are included as
 * well in a non-temporary list. include_shared has no relevance when building
 * a list of temporary relations.
 */
static List *
BuildRelationList(bool temp_relations, bool include_shared)
{
    List       *RelationList = NIL;
    Relation    rel;
    TableScanDesc scan;
    HeapTuple   tup;
    MemoryContext ctx = CurrentMemoryContext;
    MemoryContext oldctx;
 
    StartTransactionCommand();
 
    rel = table_open(RelationRelationId, AccessShareLock);
    scan = table_beginscan_catalog(rel, 0, NULL);
 
    while (HeapTupleIsValid(tup = heap_getnext(scan, ForwardScanDirection)))
    {
        Form_pg_class pgc = (Form_pg_class) GETSTRUCT(tup);
 
        if (!RELKIND_HAS_STORAGE(pgc->relkind))
            continue;
 
        /* Only include temporary relations when explicitly asked to */
        if (pgc->relpersistence == RELPERSISTENCE_TEMP)
        {
            if (!temp_relations)
                continue;
        }
        else
        {
            /*
             * If we are only interested in temp relations then continue
             * immediately as the current relation isn't a temp relation.
             */
            if (temp_relations)
                continue;
 
            if (pgc->relisshared && !include_shared)
                continue;
        }
 
        oldctx = MemoryContextSwitchTo(ctx);
        RelationList = lappend_oid(RelationList, pgc->oid);
        MemoryContextSwitchTo(oldctx);
    }
 
    table_endscan(scan);
    table_close(rel, AccessShareLock);
 
    CommitTransactionCommand();
 
    return RelationList;
}
 
/*
 * DataChecksumsWorkerMain
 *
 * Main function for enabling checksums in a single database. This is the
 * function set as the bgw_function_name in the dynamic background worker
 * process initiated for each database by the worker launcher. After enabling
 * data checksums in each applicable relation in the database, it will wait for
 * all temporary relations that were present when the function started to
 * disappear before returning. This is required since we cannot rewrite
 * existing temporary relations with data checksums.
 */
void
DataChecksumsWorkerMain(Datum arg)
{
    Oid         dboid;
    List       *RelationList = NIL;
    List       *InitialTempTableList = NIL;
    BufferAccessStrategy strategy;
    bool        aborted = false;
    int64       rels_done;
    bool        process_shared;
#ifdef USE_INJECTION_POINTS
    bool        retried = false;
#endif
 
    worker_invocation = DatumGetUInt64(arg);
 
    operation = ENABLE_DATACHECKSUMS;
 
    pqsignal(SIGTERM, die);
    pqsignal(SIGUSR1, procsignal_sigusr1_handler);
 
    BackgroundWorkerUnblockSignals();
 
    MyBackendType = B_DATACHECKSUMSWORKER_WORKER;
    init_ps_display(NULL);
 
    LWLockAcquire(DataChecksumsWorkerLock, LW_SHARED);
    if (DataChecksumState->worker_invocation != worker_invocation)
    {
        LWLockRelease(DataChecksumsWorkerLock);
        return;
    }
    dboid = DataChecksumState->database_oid;
    LWLockRelease(DataChecksumsWorkerLock);
 
    BackgroundWorkerInitializeConnectionByOid(dboid, InvalidOid,
                                              BGWORKER_BYPASS_ALLOWCONN);
 
    /* worker will have a separate entry in pg_stat_progress_data_checksums */
    pgstat_progress_start_command(PROGRESS_COMMAND_DATACHECKSUMS,
                                  InvalidOid);
    ResetDataChecksumsProgressCounters();
 
    /*
     * Get a list of all temp tables present as we start in this database. We
     * need to wait until they are all gone before we exit.  For the list of
     * relations to enable checksums in, check if shared catalogs have been
     * processed already.
     */
    InitialTempTableList = BuildRelationList(true, false);
    LWLockAcquire(DataChecksumsWorkerLock, LW_EXCLUSIVE);
    if (DataChecksumState->worker_invocation != worker_invocation)
    {
        LWLockRelease(DataChecksumsWorkerLock);
        return;
    }
    process_shared = DataChecksumState->process_shared_catalogs;
 
    /*
     * Enable vacuum cost delay, if any.  While this process isn't doing any
     * vacuuming, we are re-using the infrastructure that vacuum cost delay
     * provides rather than inventing something bespoke. This is an internal
     * implementation detail and care should be taken to avoid it bleeding
     * through to the user to avoid confusion.
     *
     * VacuumUpdateCosts() propagates the values to the variables actually
     * read by vacuum_delay_point().
     */
    VacuumCostDelay = DataChecksumState->cost_delay;
    VacuumCostLimit = DataChecksumState->cost_limit;
    LWLockRelease(DataChecksumsWorkerLock);
    VacuumUpdateCosts();
    VacuumCostBalance = 0;
 
    /*
     * Create and set the vacuum strategy as our buffer strategy.
     */
    strategy = GetAccessStrategy(BAS_VACUUM);
 
    RelationList = BuildRelationList(false, process_shared);
 
    /* Update the total number of relations to be processed in this DB. */
    {
        const int   index[] = {
            PROGRESS_DATACHECKSUMS_RELS_TOTAL,
            PROGRESS_DATACHECKSUMS_RELS_DONE
        };
 
        int64       vals[2];
 
        vals[0] = list_length(RelationList);
        vals[1] = 0;
 
        pgstat_progress_update_multi_param(2, index, vals);
    }
 
    /* Process the relations */
    rels_done = 0;
    foreach_oid(reloid, RelationList)
    {
        bool        costs_updated = false;
 
        if (!ProcessSingleRelationByOid(reloid, strategy))
        {
            aborted = true;
            break;
        }
 
        pgstat_progress_update_param(PROGRESS_DATACHECKSUMS_RELS_DONE,
                                     ++rels_done);
        CHECK_FOR_INTERRUPTS();
        CHECK_FOR_WORKER_ABORT_REQUEST();
 
        if (abort_requested)
            break;
 
        /*
         * Check if the cost settings changed during runtime and if so, update
         * to reflect the new values and signal that the access strategy needs
         * to be refreshed.
         */
        LWLockAcquire(DataChecksumsWorkerLock, LW_EXCLUSIVE);
        if (DataChecksumState->worker_invocation != worker_invocation)
        {
            LWLockRelease(DataChecksumsWorkerLock);
            break;
        }
        if ((DataChecksumState->launch_cost_delay != DataChecksumState->cost_delay)
            || (DataChecksumState->launch_cost_limit != DataChecksumState->cost_limit))
        {
            costs_updated = true;
            VacuumCostDelay = DataChecksumState->launch_cost_delay;
            VacuumCostLimit = DataChecksumState->launch_cost_limit;
            VacuumUpdateCosts();
 
            DataChecksumState->cost_delay = DataChecksumState->launch_cost_delay;
            DataChecksumState->cost_limit = DataChecksumState->launch_cost_limit;
        }
        else
            costs_updated = false;
        LWLockRelease(DataChecksumsWorkerLock);
 
        if (costs_updated)
        {
            FreeAccessStrategy(strategy);
            strategy = GetAccessStrategy(BAS_VACUUM);
        }
    }
 
    list_free(RelationList);
    FreeAccessStrategy(strategy);
 
    if (aborted || abort_requested)
    {
        LWLockAcquire(DataChecksumsWorkerLock, LW_EXCLUSIVE);
        if (DataChecksumState->worker_invocation == worker_invocation)
            DataChecksumState->worker_result = DATACHECKSUMSWORKER_ABORTED;
        LWLockRelease(DataChecksumsWorkerLock);
        ereport(DEBUG1,
                errmsg("data checksum processing aborted in database OID %u",
                       dboid));
        return;
    }
 
    /* The worker is about to wait for temporary tables to go away. */
    pgstat_progress_update_param(PROGRESS_DATACHECKSUMS_PHASE,
                                 PROGRESS_DATACHECKSUMS_PHASE_WAITING_TEMPREL);
 
    /*
     * Wait for all temp tables that existed when we started to go away. This
     * is necessary since we cannot "reach" them to enable checksums. Any temp
     * tables created after we started will already have checksums in them
     * (due to the "inprogress-on" state), so no need to wait for those.
     */
    for (;;)
    {
        List       *CurrentTempTables;
        int         numleft;
        char        activity[64];
 
        CurrentTempTables = BuildRelationList(true, false);
        numleft = 0;
        foreach_oid(tmptbloid, InitialTempTableList)
        {
            if (list_member_oid(CurrentTempTables, tmptbloid))
                numleft++;
        }
        list_free(CurrentTempTables);
 
#ifdef USE_INJECTION_POINTS
        if (IS_INJECTION_POINT_ATTACHED("datachecksumsworker-fake-temptable-wait"))
        {
            /* Make sure to just cause one retry */
            if (!retried && numleft == 0)
            {
                numleft = 1;
                retried = true;
 
                INJECTION_POINT_CACHED("datachecksumsworker-fake-temptable-wait", NULL);
            }
        }
#endif
 
        if (numleft == 0)
            break;
 
        /*
         * At least one temp table is left to wait for, indicate in pgstat
         * activity and progress reporting.
         */
        snprintf(activity,
                 sizeof(activity),
                 "Waiting for %d temp tables to be removed", numleft);
        pgstat_report_activity(STATE_RUNNING, activity);
 
        /* Retry every 3 seconds */
        ResetLatch(MyLatch);
        (void) WaitLatch(MyLatch,
                         WL_LATCH_SET | WL_TIMEOUT | WL_EXIT_ON_PM_DEATH,
                         3000,
                         WAIT_EVENT_CHECKSUM_ENABLE_TEMPTABLE_WAIT);
 
        CHECK_FOR_INTERRUPTS();
        CHECK_FOR_WORKER_ABORT_REQUEST();
 
        if (aborted || abort_requested)
        {
            LWLockAcquire(DataChecksumsWorkerLock, LW_EXCLUSIVE);
            if (DataChecksumState->worker_invocation == worker_invocation)
                DataChecksumState->worker_result = DATACHECKSUMSWORKER_ABORTED;
            LWLockRelease(DataChecksumsWorkerLock);
            ereport(LOG,
                    errmsg("data checksum processing aborted in database OID %u",
                           dboid));
            return;
        }
    }
 
    list_free(InitialTempTableList);
 
    /* worker done */
    pgstat_progress_end_command();
 
    LWLockAcquire(DataChecksumsWorkerLock, LW_EXCLUSIVE);
    if (DataChecksumState->worker_invocation == worker_invocation)
        DataChecksumState->worker_result = DATACHECKSUMSWORKER_SUCCESSFUL;
    LWLockRelease(DataChecksumsWorkerLock);
}