pg_walinspect.c

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/*-------------------------------------------------------------------------
 *
 * pg_walinspect.c
 *        Functions to inspect contents of PostgreSQL Write-Ahead Log
 *
 * Copyright (c) 2022-2026, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *        contrib/pg_walinspect/pg_walinspect.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"
 
#include "access/htup_details.h"
#include "access/xlog.h"
#include "access/xlog_internal.h"
#include "access/xlogreader.h"
#include "access/xlogrecovery.h"
#include "access/xlogstats.h"
#include "access/xlogutils.h"
#include "funcapi.h"
#include "miscadmin.h"
#include "port/pg_bitutils.h"
#include "utils/array.h"
#include "utils/builtins.h"
#include "utils/pg_lsn.h"
#include "utils/tuplestore.h"
 
/*
 * NOTE: For any code change or issue fix here, it is highly recommended to
 * give a thought about doing the same in pg_waldump tool as well.
 */
 
PG_MODULE_MAGIC_EXT(
                    .name = "pg_walinspect",
                    .version = PG_VERSION
);
 
PG_FUNCTION_INFO_V1(pg_get_wal_block_info);
PG_FUNCTION_INFO_V1(pg_get_wal_record_info);
PG_FUNCTION_INFO_V1(pg_get_wal_records_info);
PG_FUNCTION_INFO_V1(pg_get_wal_records_info_till_end_of_wal);
PG_FUNCTION_INFO_V1(pg_get_wal_stats);
PG_FUNCTION_INFO_V1(pg_get_wal_stats_till_end_of_wal);
 
static void ValidateInputLSNs(XLogRecPtr start_lsn, XLogRecPtr *end_lsn);
static XLogRecPtr GetCurrentLSN(void);
static XLogReaderState *InitXLogReaderState(XLogRecPtr lsn);
static XLogRecord *ReadNextXLogRecord(XLogReaderState *xlogreader);
static void GetWALRecordInfo(XLogReaderState *record, Datum *values,
                             bool *nulls, uint32 ncols);
static void GetWALRecordsInfo(FunctionCallInfo fcinfo,
                              XLogRecPtr start_lsn,
                              XLogRecPtr end_lsn);
static void GetXLogSummaryStats(XLogStats *stats, ReturnSetInfo *rsinfo,
                                Datum *values, bool *nulls, uint32 ncols,
                                bool stats_per_record);
static void FillXLogStatsRow(const char *name, uint64 n, uint64 total_count,
                             uint64 rec_len, uint64 total_rec_len,
                             uint64 fpi_len, uint64 total_fpi_len,
                             uint64 tot_len, uint64 total_len,
                             Datum *values, bool *nulls, uint32 ncols);
static void GetWalStats(FunctionCallInfo fcinfo,
                        XLogRecPtr start_lsn,
                        XLogRecPtr end_lsn,
                        bool stats_per_record);
static void GetWALBlockInfo(FunctionCallInfo fcinfo, XLogReaderState *record,
                            bool show_data);
 
/*
 * Return the LSN up to which the server has WAL.
 */
static XLogRecPtr
GetCurrentLSN(void)
{
    XLogRecPtr  curr_lsn;
 
    /*
     * We determine the current LSN of the server similar to how page_read
     * callback read_local_xlog_page_no_wait does.
     */
    if (!RecoveryInProgress())
        curr_lsn = GetFlushRecPtr(NULL);
    else
        curr_lsn = GetXLogReplayRecPtr(NULL);
 
    Assert(XLogRecPtrIsValid(curr_lsn));
 
    return curr_lsn;
}
 
/*
 * Initialize WAL reader and identify first valid LSN.
 */
static XLogReaderState *
InitXLogReaderState(XLogRecPtr lsn)
{
    XLogReaderState *xlogreader;
    ReadLocalXLogPageNoWaitPrivate *private_data;
    XLogRecPtr  first_valid_record;
    char       *errormsg;
 
    /*
     * Reading WAL below the first page of the first segments isn't allowed.
     * This is a bootstrap WAL page and the page_read callback fails to read
     * it.
     */
    if (lsn < XLOG_BLCKSZ)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("could not read WAL at LSN %X/%08X",
                        LSN_FORMAT_ARGS(lsn))));
 
    private_data = palloc0_object(ReadLocalXLogPageNoWaitPrivate);
 
    xlogreader = XLogReaderAllocate(wal_segment_size, NULL,
                                    XL_ROUTINE(.page_read = &read_local_xlog_page_no_wait,
                                               .segment_open = &wal_segment_open,
                                               .segment_close = &wal_segment_close),
                                    private_data);
 
    if (xlogreader == NULL)
        ereport(ERROR,
                (errcode(ERRCODE_OUT_OF_MEMORY),
                 errmsg("out of memory"),
                 errdetail("Failed while allocating a WAL reading processor.")));
 
    /* first find a valid recptr to start from */
    first_valid_record = XLogFindNextRecord(xlogreader, lsn, &errormsg);
 
    if (!XLogRecPtrIsValid(first_valid_record))
    {
        if (errormsg)
            ereport(ERROR,
                    errmsg("could not find a valid record after %X/%08X: %s",
                           LSN_FORMAT_ARGS(lsn), errormsg));
        else
            ereport(ERROR,
                    errmsg("could not find a valid record after %X/%08X",
                           LSN_FORMAT_ARGS(lsn)));
    }
 
    return xlogreader;
}
 
/*
 * Read next WAL record.
 *
 * By design, to be less intrusive in a running system, no slot is allocated
 * to reserve the WAL we're about to read. Therefore this function can
 * encounter read errors for historical WAL.
 *
 * We guard against ordinary errors trying to read WAL that hasn't been
 * written yet by limiting end_lsn to the flushed WAL, but that can also
 * encounter errors if the flush pointer falls in the middle of a record. In
 * that case we'll return NULL.
 */
static XLogRecord *
ReadNextXLogRecord(XLogReaderState *xlogreader)
{
    XLogRecord *record;
    char       *errormsg;
 
    record = XLogReadRecord(xlogreader, &errormsg);
 
    if (record == NULL)
    {
        ReadLocalXLogPageNoWaitPrivate *private_data;
 
        /* return NULL, if end of WAL is reached */
        private_data = (ReadLocalXLogPageNoWaitPrivate *)
            xlogreader->private_data;
 
        if (private_data->end_of_wal)
            return NULL;
 
        if (errormsg)
            ereport(ERROR,
                    (errcode_for_file_access(),
                     errmsg("could not read WAL at %X/%08X: %s",
                            LSN_FORMAT_ARGS(xlogreader->EndRecPtr), errormsg)));
        else
            ereport(ERROR,
                    (errcode_for_file_access(),
                     errmsg("could not read WAL at %X/%08X",
                            LSN_FORMAT_ARGS(xlogreader->EndRecPtr))));
    }
 
    return record;
}
 
/*
 * Output values that make up a row describing caller's WAL record.
 *
 * This function leaks memory.  Caller may need to use its own custom memory
 * context.
 *
 * Keep this in sync with GetWALBlockInfo.
 */
static void
GetWALRecordInfo(XLogReaderState *record, Datum *values,
                 bool *nulls, uint32 ncols)
{
    const char *record_type;
    RmgrData    desc;
    uint32      fpi_len = 0;
    StringInfoData rec_desc;
    StringInfoData rec_blk_ref;
    int         i = 0;
 
    desc = GetRmgr(XLogRecGetRmid(record));
    record_type = desc.rm_identify(XLogRecGetInfo(record));
 
    if (record_type == NULL)
        record_type = psprintf("UNKNOWN (%x)", XLogRecGetInfo(record) & ~XLR_INFO_MASK);
 
    initStringInfo(&rec_desc);
    desc.rm_desc(&rec_desc, record);
 
    if (XLogRecHasAnyBlockRefs(record))
    {
        initStringInfo(&rec_blk_ref);
        XLogRecGetBlockRefInfo(record, false, true, &rec_blk_ref, &fpi_len);
    }
 
    values[i++] = LSNGetDatum(record->ReadRecPtr);
    values[i++] = LSNGetDatum(record->EndRecPtr);
    values[i++] = LSNGetDatum(XLogRecGetPrev(record));
    values[i++] = TransactionIdGetDatum(XLogRecGetXid(record));
    values[i++] = CStringGetTextDatum(desc.rm_name);
    values[i++] = CStringGetTextDatum(record_type);
    values[i++] = UInt32GetDatum(XLogRecGetTotalLen(record));
    values[i++] = UInt32GetDatum(XLogRecGetDataLen(record));
    values[i++] = UInt32GetDatum(fpi_len);
 
    if (rec_desc.len > 0)
        values[i++] = CStringGetTextDatum(rec_desc.data);
    else
        nulls[i++] = true;
 
    if (XLogRecHasAnyBlockRefs(record))
        values[i++] = CStringGetTextDatum(rec_blk_ref.data);
    else
        nulls[i++] = true;
 
    Assert(i == ncols);
}
 
 
/*
 * Output one or more rows in rsinfo tuple store, each describing a single
 * block reference from caller's WAL record. (Should only be called with
 * records that have block references.)
 *
 * This function leaks memory.  Caller may need to use its own custom memory
 * context.
 *
 * Keep this in sync with GetWALRecordInfo.
 */
static void
GetWALBlockInfo(FunctionCallInfo fcinfo, XLogReaderState *record,
                bool show_data)
{
#define PG_GET_WAL_BLOCK_INFO_COLS 20
    int         block_id;
    ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
    RmgrData    desc;
    const char *record_type;
    StringInfoData rec_desc;
 
    Assert(XLogRecHasAnyBlockRefs(record));
 
    desc = GetRmgr(XLogRecGetRmid(record));
    record_type = desc.rm_identify(XLogRecGetInfo(record));
 
    if (record_type == NULL)
        record_type = psprintf("UNKNOWN (%x)",
                               XLogRecGetInfo(record) & ~XLR_INFO_MASK);
 
    initStringInfo(&rec_desc);
    desc.rm_desc(&rec_desc, record);
 
    for (block_id = 0; block_id <= XLogRecMaxBlockId(record); block_id++)
    {
        DecodedBkpBlock *blk;
        BlockNumber blkno;
        RelFileLocator rnode;
        ForkNumber  forknum;
        Datum       values[PG_GET_WAL_BLOCK_INFO_COLS] = {0};
        bool        nulls[PG_GET_WAL_BLOCK_INFO_COLS] = {0};
        uint32      block_data_len = 0,
                    block_fpi_len = 0;
        ArrayType  *block_fpi_info = NULL;
        int         i = 0;
 
        if (!XLogRecHasBlockRef(record, block_id))
            continue;
 
        blk = XLogRecGetBlock(record, block_id);
 
        (void) XLogRecGetBlockTagExtended(record, block_id,
                                          &rnode, &forknum, &blkno, NULL);
 
        /* Save block_data_len */
        if (blk->has_data)
            block_data_len = blk->data_len;
 
        if (blk->has_image)
        {
            /* Block reference has an FPI, so prepare relevant output */
            int         bitcnt;
            int         cnt = 0;
            Datum      *flags;
 
            /* Save block_fpi_len */
            block_fpi_len = blk->bimg_len;
 
            /* Construct and save block_fpi_info */
            bitcnt = pg_popcount((const char *) &blk->bimg_info,
                                 sizeof(uint8));
            flags = palloc0_array(Datum, bitcnt);
            if ((blk->bimg_info & BKPIMAGE_HAS_HOLE) != 0)
                flags[cnt++] = CStringGetTextDatum("HAS_HOLE");
            if (blk->apply_image)
                flags[cnt++] = CStringGetTextDatum("APPLY");
            if ((blk->bimg_info & BKPIMAGE_COMPRESS_PGLZ) != 0)
                flags[cnt++] = CStringGetTextDatum("COMPRESS_PGLZ");
            if ((blk->bimg_info & BKPIMAGE_COMPRESS_LZ4) != 0)
                flags[cnt++] = CStringGetTextDatum("COMPRESS_LZ4");
            if ((blk->bimg_info & BKPIMAGE_COMPRESS_ZSTD) != 0)
                flags[cnt++] = CStringGetTextDatum("COMPRESS_ZSTD");
 
            Assert(cnt <= bitcnt);
            block_fpi_info = construct_array_builtin(flags, cnt, TEXTOID);
        }
 
        /* start_lsn, end_lsn, prev_lsn, and blockid outputs */
        values[i++] = LSNGetDatum(record->ReadRecPtr);
        values[i++] = LSNGetDatum(record->EndRecPtr);
        values[i++] = LSNGetDatum(XLogRecGetPrev(record));
        values[i++] = Int16GetDatum(block_id);
 
        /* relfile and block related outputs */
        values[i++] = ObjectIdGetDatum(blk->rlocator.spcOid);
        values[i++] = ObjectIdGetDatum(blk->rlocator.dbOid);
        values[i++] = ObjectIdGetDatum(blk->rlocator.relNumber);
        values[i++] = Int16GetDatum(forknum);
        values[i++] = Int64GetDatum((int64) blkno);
 
        /* xid, resource_manager, and record_type outputs */
        values[i++] = TransactionIdGetDatum(XLogRecGetXid(record));
        values[i++] = CStringGetTextDatum(desc.rm_name);
        values[i++] = CStringGetTextDatum(record_type);
 
        /*
         * record_length, main_data_length, block_data_len, and
         * block_fpi_length outputs
         */
        values[i++] = UInt32GetDatum(XLogRecGetTotalLen(record));
        values[i++] = UInt32GetDatum(XLogRecGetDataLen(record));
        values[i++] = UInt32GetDatum(block_data_len);
        values[i++] = UInt32GetDatum(block_fpi_len);
 
        /* block_fpi_info (text array) output */
        if (block_fpi_info)
            values[i++] = PointerGetDatum(block_fpi_info);
        else
            nulls[i++] = true;
 
        /* description output (describes WAL record) */
        if (rec_desc.len > 0)
            values[i++] = CStringGetTextDatum(rec_desc.data);
        else
            nulls[i++] = true;
 
        /* block_data output */
        if (blk->has_data && show_data)
        {
            bytea      *block_data;
 
            block_data = (bytea *) palloc(block_data_len + VARHDRSZ);
            SET_VARSIZE(block_data, block_data_len + VARHDRSZ);
            memcpy(VARDATA(block_data), blk->data, block_data_len);
            values[i++] = PointerGetDatum(block_data);
        }
        else
            nulls[i++] = true;
 
        /* block_fpi_data output */
        if (blk->has_image && show_data)
        {
            PGAlignedBlock buf;
            Page        page;
            bytea      *block_fpi_data;
 
            page = (Page) buf.data;
            if (!RestoreBlockImage(record, block_id, page))
                ereport(ERROR,
                        (errcode(ERRCODE_INTERNAL_ERROR),
                         errmsg_internal("%s", record->errormsg_buf)));
 
            block_fpi_data = (bytea *) palloc(BLCKSZ + VARHDRSZ);
            SET_VARSIZE(block_fpi_data, BLCKSZ + VARHDRSZ);
            memcpy(VARDATA(block_fpi_data), page, BLCKSZ);
            values[i++] = PointerGetDatum(block_fpi_data);
        }
        else
            nulls[i++] = true;
 
        Assert(i == PG_GET_WAL_BLOCK_INFO_COLS);
 
        /* Store a tuple for this block reference */
        tuplestore_putvalues(rsinfo->setResult, rsinfo->setDesc,
                             values, nulls);
    }
 
#undef PG_GET_WAL_BLOCK_INFO_COLS
}
 
/*
 * Get WAL record info, unnested by block reference
 */
Datum
pg_get_wal_block_info(PG_FUNCTION_ARGS)
{
    XLogRecPtr  start_lsn = PG_GETARG_LSN(0);
    XLogRecPtr  end_lsn = PG_GETARG_LSN(1);
    bool        show_data = PG_GETARG_BOOL(2);
    XLogReaderState *xlogreader;
    MemoryContext old_cxt;
    MemoryContext tmp_cxt;
 
    ValidateInputLSNs(start_lsn, &end_lsn);
 
    InitMaterializedSRF(fcinfo, 0);
 
    xlogreader = InitXLogReaderState(start_lsn);
 
    tmp_cxt = AllocSetContextCreate(CurrentMemoryContext,
                                    "pg_get_wal_block_info temporary cxt",
                                    ALLOCSET_DEFAULT_SIZES);
 
    while (ReadNextXLogRecord(xlogreader) &&
           xlogreader->EndRecPtr <= end_lsn)
    {
        CHECK_FOR_INTERRUPTS();
 
        if (!XLogRecHasAnyBlockRefs(xlogreader))
            continue;
 
        /* Use the tmp context so we can clean up after each tuple is done */
        old_cxt = MemoryContextSwitchTo(tmp_cxt);
 
        GetWALBlockInfo(fcinfo, xlogreader, show_data);
 
        /* clean up and switch back */
        MemoryContextSwitchTo(old_cxt);
        MemoryContextReset(tmp_cxt);
    }
 
    MemoryContextDelete(tmp_cxt);
    pfree(xlogreader->private_data);
    XLogReaderFree(xlogreader);
 
    PG_RETURN_VOID();
}
 
/*
 * Get WAL record info.
 */
Datum
pg_get_wal_record_info(PG_FUNCTION_ARGS)
{
#define PG_GET_WAL_RECORD_INFO_COLS 11
    Datum       result;
    Datum       values[PG_GET_WAL_RECORD_INFO_COLS] = {0};
    bool        nulls[PG_GET_WAL_RECORD_INFO_COLS] = {0};
    XLogRecPtr  lsn;
    XLogRecPtr  curr_lsn;
    XLogReaderState *xlogreader;
    TupleDesc   tupdesc;
    HeapTuple   tuple;
 
    lsn = PG_GETARG_LSN(0);
    curr_lsn = GetCurrentLSN();
 
    if (lsn > curr_lsn)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("WAL input LSN must be less than current LSN"),
                 errdetail("Current WAL LSN on the database system is at %X/%08X.",
                           LSN_FORMAT_ARGS(curr_lsn))));
 
    /* 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");
 
    xlogreader = InitXLogReaderState(lsn);
 
    if (!ReadNextXLogRecord(xlogreader))
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("could not read WAL at %X/%08X",
                        LSN_FORMAT_ARGS(xlogreader->EndRecPtr))));
 
    GetWALRecordInfo(xlogreader, values, nulls, PG_GET_WAL_RECORD_INFO_COLS);
 
    pfree(xlogreader->private_data);
    XLogReaderFree(xlogreader);
 
    tuple = heap_form_tuple(tupdesc, values, nulls);
    result = HeapTupleGetDatum(tuple);
 
    PG_RETURN_DATUM(result);
#undef PG_GET_WAL_RECORD_INFO_COLS
}
 
/*
 * Validate start and end LSNs coming from the function inputs.
 *
 * If end_lsn is found to be higher than the current LSN reported by the
 * cluster, use the current LSN as the upper bound.
 */
static void
ValidateInputLSNs(XLogRecPtr start_lsn, XLogRecPtr *end_lsn)
{
    XLogRecPtr  curr_lsn = GetCurrentLSN();
 
    if (start_lsn > curr_lsn)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("WAL start LSN must be less than current LSN"),
                 errdetail("Current WAL LSN on the database system is at %X/%08X.",
                           LSN_FORMAT_ARGS(curr_lsn))));
 
    if (start_lsn > *end_lsn)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("WAL start LSN must be less than end LSN")));
 
    if (*end_lsn > curr_lsn)
        *end_lsn = curr_lsn;
}
 
/*
 * Get info of all WAL records between start LSN and end LSN.
 */
static void
GetWALRecordsInfo(FunctionCallInfo fcinfo, XLogRecPtr start_lsn,
                  XLogRecPtr end_lsn)
{
#define PG_GET_WAL_RECORDS_INFO_COLS 11
    XLogReaderState *xlogreader;
    ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
    MemoryContext old_cxt;
    MemoryContext tmp_cxt;
 
    Assert(start_lsn <= end_lsn);
 
    InitMaterializedSRF(fcinfo, 0);
 
    xlogreader = InitXLogReaderState(start_lsn);
 
    tmp_cxt = AllocSetContextCreate(CurrentMemoryContext,
                                    "GetWALRecordsInfo temporary cxt",
                                    ALLOCSET_DEFAULT_SIZES);
 
    while (ReadNextXLogRecord(xlogreader) &&
           xlogreader->EndRecPtr <= end_lsn)
    {
        Datum       values[PG_GET_WAL_RECORDS_INFO_COLS] = {0};
        bool        nulls[PG_GET_WAL_RECORDS_INFO_COLS] = {0};
 
        /* Use the tmp context so we can clean up after each tuple is done */
        old_cxt = MemoryContextSwitchTo(tmp_cxt);
 
        GetWALRecordInfo(xlogreader, values, nulls,
                         PG_GET_WAL_RECORDS_INFO_COLS);
 
        tuplestore_putvalues(rsinfo->setResult, rsinfo->setDesc,
                             values, nulls);
 
        /* clean up and switch back */
        MemoryContextSwitchTo(old_cxt);
        MemoryContextReset(tmp_cxt);
 
        CHECK_FOR_INTERRUPTS();
    }
 
    MemoryContextDelete(tmp_cxt);
    pfree(xlogreader->private_data);
    XLogReaderFree(xlogreader);
 
#undef PG_GET_WAL_RECORDS_INFO_COLS
}
 
/*
 * Get info of all WAL records between start LSN and end LSN.
 */
Datum
pg_get_wal_records_info(PG_FUNCTION_ARGS)
{
    XLogRecPtr  start_lsn = PG_GETARG_LSN(0);
    XLogRecPtr  end_lsn = PG_GETARG_LSN(1);
 
    ValidateInputLSNs(start_lsn, &end_lsn);
    GetWALRecordsInfo(fcinfo, start_lsn, end_lsn);
 
    PG_RETURN_VOID();
}
 
/*
 * Fill single row of record counts and sizes for an rmgr or record.
 */
static void
FillXLogStatsRow(const char *name,
                 uint64 n, uint64 total_count,
                 uint64 rec_len, uint64 total_rec_len,
                 uint64 fpi_len, uint64 total_fpi_len,
                 uint64 tot_len, uint64 total_len,
                 Datum *values, bool *nulls, uint32 ncols)
{
    double      n_pct,
                rec_len_pct,
                fpi_len_pct,
                tot_len_pct;
    int         i = 0;
 
    n_pct = 0;
    if (total_count != 0)
        n_pct = 100 * (double) n / total_count;
 
    rec_len_pct = 0;
    if (total_rec_len != 0)
        rec_len_pct = 100 * (double) rec_len / total_rec_len;
 
    fpi_len_pct = 0;
    if (total_fpi_len != 0)
        fpi_len_pct = 100 * (double) fpi_len / total_fpi_len;
 
    tot_len_pct = 0;
    if (total_len != 0)
        tot_len_pct = 100 * (double) tot_len / total_len;
 
    values[i++] = CStringGetTextDatum(name);
    values[i++] = Int64GetDatum(n);
    values[i++] = Float8GetDatum(n_pct);
    values[i++] = Int64GetDatum(rec_len);
    values[i++] = Float8GetDatum(rec_len_pct);
    values[i++] = Int64GetDatum(fpi_len);
    values[i++] = Float8GetDatum(fpi_len_pct);
    values[i++] = Int64GetDatum(tot_len);
    values[i++] = Float8GetDatum(tot_len_pct);
 
    Assert(i == ncols);
}
 
/*
 * Get summary statistics about the records seen so far.
 */
static void
GetXLogSummaryStats(XLogStats *stats, ReturnSetInfo *rsinfo,
                    Datum *values, bool *nulls, uint32 ncols,
                    bool stats_per_record)
{
    MemoryContext old_cxt;
    MemoryContext tmp_cxt;
    uint64      total_count = 0;
    uint64      total_rec_len = 0;
    uint64      total_fpi_len = 0;
    uint64      total_len = 0;
    int         ri;
 
    /*
     * Each row shows its percentages of the total, so make a first pass to
     * calculate column totals.
     */
    for (ri = 0; ri <= RM_MAX_ID; ri++)
    {
        if (!RmgrIdIsValid(ri))
            continue;
 
        total_count += stats->rmgr_stats[ri].count;
        total_rec_len += stats->rmgr_stats[ri].rec_len;
        total_fpi_len += stats->rmgr_stats[ri].fpi_len;
    }
    total_len = total_rec_len + total_fpi_len;
 
    tmp_cxt = AllocSetContextCreate(CurrentMemoryContext,
                                    "GetXLogSummaryStats temporary cxt",
                                    ALLOCSET_DEFAULT_SIZES);
 
    for (ri = 0; ri <= RM_MAX_ID; ri++)
    {
        uint64      count;
        uint64      rec_len;
        uint64      fpi_len;
        uint64      tot_len;
        RmgrData    desc;
 
        if (!RmgrIdIsValid(ri))
            continue;
 
        if (!RmgrIdExists(ri))
            continue;
 
        desc = GetRmgr(ri);
 
        if (stats_per_record)
        {
            int         rj;
 
            for (rj = 0; rj < MAX_XLINFO_TYPES; rj++)
            {
                const char *id;
 
                count = stats->record_stats[ri][rj].count;
                rec_len = stats->record_stats[ri][rj].rec_len;
                fpi_len = stats->record_stats[ri][rj].fpi_len;
                tot_len = rec_len + fpi_len;
 
                /* Skip undefined combinations and ones that didn't occur */
                if (count == 0)
                    continue;
 
                old_cxt = MemoryContextSwitchTo(tmp_cxt);
 
                /* the upper four bits in xl_info are the rmgr's */
                id = desc.rm_identify(rj << 4);
                if (id == NULL)
                    id = psprintf("UNKNOWN (%x)", rj << 4);
 
                FillXLogStatsRow(psprintf("%s/%s", desc.rm_name, id), count,
                                 total_count, rec_len, total_rec_len, fpi_len,
                                 total_fpi_len, tot_len, total_len,
                                 values, nulls, ncols);
 
                tuplestore_putvalues(rsinfo->setResult, rsinfo->setDesc,
                                     values, nulls);
 
                /* clean up and switch back */
                MemoryContextSwitchTo(old_cxt);
                MemoryContextReset(tmp_cxt);
            }
        }
        else
        {
            count = stats->rmgr_stats[ri].count;
            rec_len = stats->rmgr_stats[ri].rec_len;
            fpi_len = stats->rmgr_stats[ri].fpi_len;
            tot_len = rec_len + fpi_len;
 
            old_cxt = MemoryContextSwitchTo(tmp_cxt);
 
            FillXLogStatsRow(desc.rm_name, count, total_count, rec_len,
                             total_rec_len, fpi_len, total_fpi_len, tot_len,
                             total_len, values, nulls, ncols);
 
            tuplestore_putvalues(rsinfo->setResult, rsinfo->setDesc,
                                 values, nulls);
 
            /* clean up and switch back */
            MemoryContextSwitchTo(old_cxt);
            MemoryContextReset(tmp_cxt);
        }
    }
 
    MemoryContextDelete(tmp_cxt);
}
 
/*
 * Get WAL stats between start LSN and end LSN.
 */
static void
GetWalStats(FunctionCallInfo fcinfo, XLogRecPtr start_lsn, XLogRecPtr end_lsn,
            bool stats_per_record)
{
#define PG_GET_WAL_STATS_COLS 9
    XLogReaderState *xlogreader;
    XLogStats   stats = {0};
    ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
    Datum       values[PG_GET_WAL_STATS_COLS] = {0};
    bool        nulls[PG_GET_WAL_STATS_COLS] = {0};
 
    Assert(start_lsn <= end_lsn);
 
    InitMaterializedSRF(fcinfo, 0);
 
    xlogreader = InitXLogReaderState(start_lsn);
 
    while (ReadNextXLogRecord(xlogreader) &&
           xlogreader->EndRecPtr <= end_lsn)
    {
        XLogRecStoreStats(&stats, xlogreader);
 
        CHECK_FOR_INTERRUPTS();
    }
 
    pfree(xlogreader->private_data);
    XLogReaderFree(xlogreader);
 
    GetXLogSummaryStats(&stats, rsinfo, values, nulls,
                        PG_GET_WAL_STATS_COLS,
                        stats_per_record);
 
#undef PG_GET_WAL_STATS_COLS
}
 
/*
 * Get stats of all WAL records between start LSN and end LSN.
 */
Datum
pg_get_wal_stats(PG_FUNCTION_ARGS)
{
    XLogRecPtr  start_lsn = PG_GETARG_LSN(0);
    XLogRecPtr  end_lsn = PG_GETARG_LSN(1);
    bool        stats_per_record = PG_GETARG_BOOL(2);
 
    ValidateInputLSNs(start_lsn, &end_lsn);
    GetWalStats(fcinfo, start_lsn, end_lsn, stats_per_record);
 
    PG_RETURN_VOID();
}
 
/*
 * The following functions have been removed in newer versions in 1.1, but
 * they are kept around for compatibility.
 */
Datum
pg_get_wal_records_info_till_end_of_wal(PG_FUNCTION_ARGS)
{
    XLogRecPtr  start_lsn = PG_GETARG_LSN(0);
    XLogRecPtr  end_lsn = GetCurrentLSN();
 
    if (start_lsn > end_lsn)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("WAL start LSN must be less than current LSN"),
                 errdetail("Current WAL LSN on the database system is at %X/%08X.",
                           LSN_FORMAT_ARGS(end_lsn))));
 
    GetWALRecordsInfo(fcinfo, start_lsn, end_lsn);
 
    PG_RETURN_VOID();
}
 
Datum
pg_get_wal_stats_till_end_of_wal(PG_FUNCTION_ARGS)
{
    XLogRecPtr  start_lsn = PG_GETARG_LSN(0);
    XLogRecPtr  end_lsn = GetCurrentLSN();
    bool        stats_per_record = PG_GETARG_BOOL(1);
 
    if (start_lsn > end_lsn)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("WAL start LSN must be less than current LSN"),
                 errdetail("Current WAL LSN on the database system is at %X/%08X.",
                           LSN_FORMAT_ARGS(end_lsn))));
 
    GetWalStats(fcinfo, start_lsn, end_lsn, stats_per_record);
 
    PG_RETURN_VOID();
}