pg_logicalinspect.c

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/*-------------------------------------------------------------------------
 *
 * pg_logicalinspect.c
 *        Functions to inspect contents of PostgreSQL logical snapshots
 *
 * Copyright (c) 2024-2025, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *        contrib/pg_logicalinspect/pg_logicalinspect.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"
 
#include "funcapi.h"
#include "replication/snapbuild_internal.h"
#include "utils/array.h"
#include "utils/builtins.h"
#include "utils/pg_lsn.h"
 
PG_MODULE_MAGIC_EXT(
                    .name = "pg_logicalinspect",
                    .version = PG_VERSION
);
 
PG_FUNCTION_INFO_V1(pg_get_logical_snapshot_meta);
PG_FUNCTION_INFO_V1(pg_get_logical_snapshot_info);
 
/* Return the description of SnapBuildState */
static const char *
get_snapbuild_state_desc(SnapBuildState state)
{
    const char *stateDesc = "unknown state";
 
    switch (state)
    {
        case SNAPBUILD_START:
            stateDesc = "start";
            break;
        case SNAPBUILD_BUILDING_SNAPSHOT:
            stateDesc = "building";
            break;
        case SNAPBUILD_FULL_SNAPSHOT:
            stateDesc = "full";
            break;
        case SNAPBUILD_CONSISTENT:
            stateDesc = "consistent";
            break;
    }
 
    return stateDesc;
}
 
/*
 * Extract the LSN from the given serialized snapshot file name.
 */
static XLogRecPtr
parse_snapshot_filename(const char *filename)
{
    uint32      hi;
    uint32      lo;
    XLogRecPtr  lsn;
    char        tmpfname[MAXPGPATH];
 
    /*
     * Extract the values to build the LSN.
     *
     * Note: Including ".snap" doesn't mean that sscanf() also does the format
     * check including the suffix. The subsequent check validates if the given
     * filename has the expected suffix.
     */
    if (sscanf(filename, "%X-%X.snap", &hi, &lo) != 2)
        goto parse_error;
 
    /*
     * Bring back the extracted LSN to the snapshot file format and compare it
     * to the given filename. This check strictly checks if the given filename
     * follows the format of the snapshot filename.
     */
    sprintf(tmpfname, "%X-%X.snap", hi, lo);
    if (strcmp(tmpfname, filename) != 0)
        goto parse_error;
 
    lsn = ((uint64) hi) << 32 | lo;
 
    return lsn;
 
parse_error:
    ereport(ERROR,
            errmsg("invalid snapshot file name \"%s\"", filename));
 
    return InvalidXLogRecPtr;   /* keep compiler quiet */
}
 
/*
 * Retrieve the logical snapshot file metadata.
 */
Datum
pg_get_logical_snapshot_meta(PG_FUNCTION_ARGS)
{
#define PG_GET_LOGICAL_SNAPSHOT_META_COLS 3
    SnapBuildOnDisk ondisk;
    HeapTuple   tuple;
    Datum       values[PG_GET_LOGICAL_SNAPSHOT_META_COLS] = {0};
    bool        nulls[PG_GET_LOGICAL_SNAPSHOT_META_COLS] = {0};
    TupleDesc   tupdesc;
    XLogRecPtr  lsn;
    int         i = 0;
    text       *filename_t = PG_GETARG_TEXT_PP(0);
 
    /* Build a tuple descriptor for our result type */
    if (get_call_result_type(fcinfo, NULL, &tupdesc) != TYPEFUNC_COMPOSITE)
        elog(ERROR, "return type must be a row type");
 
    lsn = parse_snapshot_filename(text_to_cstring(filename_t));
 
    /* Validate and restore the snapshot to 'ondisk' */
    SnapBuildRestoreSnapshot(&ondisk, lsn, CurrentMemoryContext, false);
 
    values[i++] = UInt32GetDatum(ondisk.magic);
    values[i++] = Int64GetDatum((int64) ondisk.checksum);
    values[i++] = UInt32GetDatum(ondisk.version);
 
    Assert(i == PG_GET_LOGICAL_SNAPSHOT_META_COLS);
 
    tuple = heap_form_tuple(tupdesc, values, nulls);
 
    PG_RETURN_DATUM(HeapTupleGetDatum(tuple));
 
#undef PG_GET_LOGICAL_SNAPSHOT_META_COLS
}
 
Datum
pg_get_logical_snapshot_info(PG_FUNCTION_ARGS)
{
#define PG_GET_LOGICAL_SNAPSHOT_INFO_COLS 14
    SnapBuildOnDisk ondisk;
    HeapTuple   tuple;
    Datum       values[PG_GET_LOGICAL_SNAPSHOT_INFO_COLS] = {0};
    bool        nulls[PG_GET_LOGICAL_SNAPSHOT_INFO_COLS] = {0};
    TupleDesc   tupdesc;
    XLogRecPtr  lsn;
    int         i = 0;
    text       *filename_t = PG_GETARG_TEXT_PP(0);
 
    /* Build a tuple descriptor for our result type */
    if (get_call_result_type(fcinfo, NULL, &tupdesc) != TYPEFUNC_COMPOSITE)
        elog(ERROR, "return type must be a row type");
 
    lsn = parse_snapshot_filename(text_to_cstring(filename_t));
 
    /* Validate and restore the snapshot to 'ondisk' */
    SnapBuildRestoreSnapshot(&ondisk, lsn, CurrentMemoryContext, false);
 
    values[i++] = CStringGetTextDatum(get_snapbuild_state_desc(ondisk.builder.state));
    values[i++] = TransactionIdGetDatum(ondisk.builder.xmin);
    values[i++] = TransactionIdGetDatum(ondisk.builder.xmax);
    values[i++] = LSNGetDatum(ondisk.builder.start_decoding_at);
    values[i++] = LSNGetDatum(ondisk.builder.two_phase_at);
    values[i++] = TransactionIdGetDatum(ondisk.builder.initial_xmin_horizon);
    values[i++] = BoolGetDatum(ondisk.builder.building_full_snapshot);
    values[i++] = BoolGetDatum(ondisk.builder.in_slot_creation);
    values[i++] = LSNGetDatum(ondisk.builder.last_serialized_snapshot);
    values[i++] = TransactionIdGetDatum(ondisk.builder.next_phase_at);
 
    values[i++] = UInt32GetDatum(ondisk.builder.committed.xcnt);
    if (ondisk.builder.committed.xcnt > 0)
    {
        Datum      *arrayelems;
 
        arrayelems = (Datum *) palloc(ondisk.builder.committed.xcnt * sizeof(Datum));
 
        for (int j = 0; j < ondisk.builder.committed.xcnt; j++)
            arrayelems[j] = TransactionIdGetDatum(ondisk.builder.committed.xip[j]);
 
        values[i++] = PointerGetDatum(construct_array_builtin(arrayelems,
                                                              ondisk.builder.committed.xcnt,
                                                              XIDOID));
    }
    else
        nulls[i++] = true;
 
    values[i++] = UInt32GetDatum(ondisk.builder.catchange.xcnt);
    if (ondisk.builder.catchange.xcnt > 0)
    {
        Datum      *arrayelems;
 
        arrayelems = (Datum *) palloc(ondisk.builder.catchange.xcnt * sizeof(Datum));
 
        for (int j = 0; j < ondisk.builder.catchange.xcnt; j++)
            arrayelems[j] = TransactionIdGetDatum(ondisk.builder.catchange.xip[j]);
 
        values[i++] = PointerGetDatum(construct_array_builtin(arrayelems,
                                                              ondisk.builder.catchange.xcnt,
                                                              XIDOID));
    }
    else
        nulls[i++] = true;
 
    Assert(i == PG_GET_LOGICAL_SNAPSHOT_INFO_COLS);
 
    tuple = heap_form_tuple(tupdesc, values, nulls);
 
    PG_RETURN_DATUM(HeapTupleGetDatum(tuple));
 
#undef PG_GET_LOGICAL_SNAPSHOT_INFO_COLS
}