timeline.c

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/*-------------------------------------------------------------------------
 *
 * timeline.c
 *    timeline-related functions.
 *
 * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
 *
 *-------------------------------------------------------------------------
 */
#include "postgres_fe.h"
 
#include "access/timeline.h"
#include "pg_rewind.h"
 
/*
 * This is copy-pasted from the backend readTimeLineHistory, modified to
 * return a malloc'd array and to work without backend functions.
 */
/*
 * Try to read a timeline's history file.
 *
 * If successful, return the list of component TLIs (the given TLI followed by
 * its ancestor TLIs).  If we can't find the history file, assume that the
 * timeline has no parents, and return a list of just the specified timeline
 * ID.
 */
TimeLineHistoryEntry *
rewind_parseTimeLineHistory(char *buffer, TimeLineID targetTLI, int *nentries)
{
    char       *fline;
    TimeLineHistoryEntry *entry;
    TimeLineHistoryEntry *entries = NULL;
    int         nlines = 0;
    TimeLineID  lasttli = 0;
    XLogRecPtr  prevend;
    char       *bufptr;
    bool        lastline = false;
 
    /*
     * Parse the file...
     */
    prevend = InvalidXLogRecPtr;
    bufptr = buffer;
    while (!lastline)
    {
        char       *ptr;
        TimeLineID  tli;
        uint32      switchpoint_hi;
        uint32      switchpoint_lo;
        int         nfields;
 
        fline = bufptr;
        while (*bufptr && *bufptr != '\n')
            bufptr++;
        if (!(*bufptr))
            lastline = true;
        else
            *bufptr++ = '\0';
 
        /* skip leading whitespace and check for # comment */
        for (ptr = fline; *ptr; ptr++)
        {
            if (!isspace((unsigned char) *ptr))
                break;
        }
        if (*ptr == '\0' || *ptr == '#')
            continue;
 
        nfields = sscanf(fline, "%u\t%X/%X", &tli, &switchpoint_hi, &switchpoint_lo);
 
        if (nfields < 1)
        {
            /* expect a numeric timeline ID as first field of line */
            pg_log_error("syntax error in history file: %s", fline);
            pg_log_error_detail("Expected a numeric timeline ID.");
            exit(1);
        }
        if (nfields != 3)
        {
            pg_log_error("syntax error in history file: %s", fline);
            pg_log_error_detail("Expected a write-ahead log switchpoint location.");
            exit(1);
        }
        if (entries && tli <= lasttli)
        {
            pg_log_error("invalid data in history file: %s", fline);
            pg_log_error_detail("Timeline IDs must be in increasing sequence.");
            exit(1);
        }
 
        lasttli = tli;
 
        nlines++;
        entries = pg_realloc(entries, nlines * sizeof(TimeLineHistoryEntry));
 
        entry = &entries[nlines - 1];
        entry->tli = tli;
        entry->begin = prevend;
        entry->end = ((uint64) (switchpoint_hi)) << 32 | (uint64) switchpoint_lo;
        prevend = entry->end;
 
        /* we ignore the remainder of each line */
    }
 
    if (entries && targetTLI <= lasttli)
    {
        pg_log_error("invalid data in history file");
        pg_log_error_detail("Timeline IDs must be less than child timeline's ID.");
        exit(1);
    }
 
    /*
     * Create one more entry for the "tip" of the timeline, which has no entry
     * in the history file.
     */
    nlines++;
    if (entries)
        entries = pg_realloc(entries, nlines * sizeof(TimeLineHistoryEntry));
    else
        entries = pg_malloc(1 * sizeof(TimeLineHistoryEntry));
 
    entry = &entries[nlines - 1];
    entry->tli = targetTLI;
    entry->begin = prevend;
    entry->end = InvalidXLogRecPtr;
 
    *nentries = nlines;
    return entries;
}