reinit.c

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/*-------------------------------------------------------------------------
 *
 * reinit.c
 *    Reinitialization of unlogged relations
 *
 * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *    src/backend/storage/file/reinit.c
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include <unistd.h>

#include "common/relpath.h"
#include "storage/copydir.h"
#include "storage/fd.h"
#include "storage/reinit.h"
#include "utils/hsearch.h"
#include "utils/memutils.h"

static void ResetUnloggedRelationsInTablespaceDir(const char *tsdirname,
                                                  int op);
static void ResetUnloggedRelationsInDbspaceDir(const char *dbspacedirname,
                                               int op);

typedef struct
{
    Oid         reloid;         /* hash key */
} unlogged_relation_entry;

/*
 * Reset unlogged relations from before the last restart.
 *
 * If op includes UNLOGGED_RELATION_CLEANUP, we remove all forks of any
 * relation with an "init" fork, except for the "init" fork itself.
 *
 * If op includes UNLOGGED_RELATION_INIT, we copy the "init" fork to the main
 * fork.
 */
void
ResetUnloggedRelations(int op)
{
    char        temp_path[MAXPGPATH + 10 + sizeof(TABLESPACE_VERSION_DIRECTORY)];
    DIR        *spc_dir;
    struct dirent *spc_de;
    MemoryContext tmpctx,
                oldctx;

    /* Log it. */
    elog(DEBUG1, "resetting unlogged relations: cleanup %d init %d",
         (op & UNLOGGED_RELATION_CLEANUP) != 0,
         (op & UNLOGGED_RELATION_INIT) != 0);

    /*
     * Just to be sure we don't leak any memory, let's create a temporary
     * memory context for this operation.
     */
    tmpctx = AllocSetContextCreate(CurrentMemoryContext,
                                   "ResetUnloggedRelations",
                                   ALLOCSET_DEFAULT_SIZES);
    oldctx = MemoryContextSwitchTo(tmpctx);

    /*
     * First process unlogged files in pg_default ($PGDATA/base)
     */
    ResetUnloggedRelationsInTablespaceDir("base", op);

    /*
     * Cycle through directories for all non-default tablespaces.
     */
    spc_dir = AllocateDir("pg_tblspc");

    while ((spc_de = ReadDir(spc_dir, "pg_tblspc")) != NULL)
    {
        if (strcmp(spc_de->d_name, ".") == 0 ||
            strcmp(spc_de->d_name, "..") == 0)
            continue;

        snprintf(temp_path, sizeof(temp_path), "pg_tblspc/%s/%s",
                 spc_de->d_name, TABLESPACE_VERSION_DIRECTORY);
        ResetUnloggedRelationsInTablespaceDir(temp_path, op);
    }

    FreeDir(spc_dir);

    /*
     * Restore memory context.
     */
    MemoryContextSwitchTo(oldctx);
    MemoryContextDelete(tmpctx);
}

/*
 * Process one tablespace directory for ResetUnloggedRelations
 */
static void
ResetUnloggedRelationsInTablespaceDir(const char *tsdirname, int op)
{
    DIR        *ts_dir;
    struct dirent *de;
    char        dbspace_path[MAXPGPATH * 2];

    ts_dir = AllocateDir(tsdirname);

    /*
     * If we get ENOENT on a tablespace directory, log it and return.  This
     * can happen if a previous DROP TABLESPACE crashed between removing the
     * tablespace directory and removing the symlink in pg_tblspc.  We don't
     * really want to prevent database startup in that scenario, so let it
     * pass instead.  Any other type of error will be reported by ReadDir
     * (causing a startup failure).
     */
    if (ts_dir == NULL && errno == ENOENT)
    {
        ereport(LOG,
                (errcode_for_file_access(),
                 errmsg("could not open directory \"%s\": %m",
                        tsdirname)));
        return;
    }

    while ((de = ReadDir(ts_dir, tsdirname)) != NULL)
    {
        /*
         * We're only interested in the per-database directories, which have
         * numeric names.  Note that this code will also (properly) ignore "."
         * and "..".
         */
        if (strspn(de->d_name, "0123456789") != strlen(de->d_name))
            continue;

        snprintf(dbspace_path, sizeof(dbspace_path), "%s/%s",
                 tsdirname, de->d_name);
        ResetUnloggedRelationsInDbspaceDir(dbspace_path, op);
    }

    FreeDir(ts_dir);
}

/*
 * Process one per-dbspace directory for ResetUnloggedRelations
 */
static void
ResetUnloggedRelationsInDbspaceDir(const char *dbspacedirname, int op)
{
    DIR        *dbspace_dir;
    struct dirent *de;
    char        rm_path[MAXPGPATH * 2];

    /* Caller must specify at least one operation. */
    Assert((op & (UNLOGGED_RELATION_CLEANUP | UNLOGGED_RELATION_INIT)) != 0);

    /*
     * Cleanup is a two-pass operation.  First, we go through and identify all
     * the files with init forks.  Then, we go through again and nuke
     * everything with the same OID except the init fork.
     */
    if ((op & UNLOGGED_RELATION_CLEANUP) != 0)
    {
        HTAB       *hash;
        HASHCTL     ctl;

        /*
         * It's possible that someone could create a ton of unlogged relations
         * in the same database & tablespace, so we'd better use a hash table
         * rather than an array or linked list to keep track of which files
         * need to be reset.  Otherwise, this cleanup operation would be
         * O(n^2).
         */
        ctl.keysize = sizeof(Oid);
        ctl.entrysize = sizeof(unlogged_relation_entry);
        ctl.hcxt = CurrentMemoryContext;
        hash = hash_create("unlogged relation OIDs", 32, &ctl,
                           HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);

        /* Scan the directory. */
        dbspace_dir = AllocateDir(dbspacedirname);
        while ((de = ReadDir(dbspace_dir, dbspacedirname)) != NULL)
        {
            ForkNumber  forkNum;
            int         oidchars;
            unlogged_relation_entry ent;

            /* Skip anything that doesn't look like a relation data file. */
            if (!parse_filename_for_nontemp_relation(de->d_name, &oidchars,
                                                     &forkNum))
                continue;

            /* Also skip it unless this is the init fork. */
            if (forkNum != INIT_FORKNUM)
                continue;

            /*
             * Put the OID portion of the name into the hash table, if it
             * isn't already.
             */
            ent.reloid = atooid(de->d_name);
            (void) hash_search(hash, &ent, HASH_ENTER, NULL);
        }

        /* Done with the first pass. */
        FreeDir(dbspace_dir);

        /*
         * If we didn't find any init forks, there's no point in continuing;
         * we can bail out now.
         */
        if (hash_get_num_entries(hash) == 0)
        {
            hash_destroy(hash);
            return;
        }

        /*
         * Now, make a second pass and remove anything that matches.
         */
        dbspace_dir = AllocateDir(dbspacedirname);
        while ((de = ReadDir(dbspace_dir, dbspacedirname)) != NULL)
        {
            ForkNumber  forkNum;
            int         oidchars;
            unlogged_relation_entry ent;

            /* Skip anything that doesn't look like a relation data file. */
            if (!parse_filename_for_nontemp_relation(de->d_name, &oidchars,
                                                     &forkNum))
                continue;

            /* We never remove the init fork. */
            if (forkNum == INIT_FORKNUM)
                continue;

            /*
             * See whether the OID portion of the name shows up in the hash
             * table.  If so, nuke it!
             */
            ent.reloid = atooid(de->d_name);
            if (hash_search(hash, &ent, HASH_FIND, NULL))
            {
                snprintf(rm_path, sizeof(rm_path), "%s/%s",
                         dbspacedirname, de->d_name);
                if (unlink(rm_path) < 0)
                    ereport(ERROR,
                            (errcode_for_file_access(),
                             errmsg("could not remove file \"%s\": %m",
                                    rm_path)));
                else
                    elog(DEBUG2, "unlinked file \"%s\"", rm_path);
            }
        }

        /* Cleanup is complete. */
        FreeDir(dbspace_dir);
        hash_destroy(hash);
    }

    /*
     * Initialization happens after cleanup is complete: we copy each init
     * fork file to the corresponding main fork file.  Note that if we are
     * asked to do both cleanup and init, we may never get here: if the
     * cleanup code determines that there are no init forks in this dbspace,
     * it will return before we get to this point.
     */
    if ((op & UNLOGGED_RELATION_INIT) != 0)
    {
        /* Scan the directory. */
        dbspace_dir = AllocateDir(dbspacedirname);
        while ((de = ReadDir(dbspace_dir, dbspacedirname)) != NULL)
        {
            ForkNumber  forkNum;
            int         oidchars;
            char        oidbuf[OIDCHARS + 1];
            char        srcpath[MAXPGPATH * 2];
            char        dstpath[MAXPGPATH];

            /* Skip anything that doesn't look like a relation data file. */
            if (!parse_filename_for_nontemp_relation(de->d_name, &oidchars,
                                                     &forkNum))
                continue;

            /* Also skip it unless this is the init fork. */
            if (forkNum != INIT_FORKNUM)
                continue;

            /* Construct source pathname. */
            snprintf(srcpath, sizeof(srcpath), "%s/%s",
                     dbspacedirname, de->d_name);

            /* Construct destination pathname. */
            memcpy(oidbuf, de->d_name, oidchars);
            oidbuf[oidchars] = '\0';
            snprintf(dstpath, sizeof(dstpath), "%s/%s%s",
                     dbspacedirname, oidbuf, de->d_name + oidchars + 1 +
                     strlen(forkNames[INIT_FORKNUM]));

            /* OK, we're ready to perform the actual copy. */
            elog(DEBUG2, "copying %s to %s", srcpath, dstpath);
            copy_file(srcpath, dstpath);
        }

        FreeDir(dbspace_dir);

        /*
         * copy_file() above has already called pg_flush_data() on the files
         * it created. Now we need to fsync those files, because a checkpoint
         * won't do it for us while we're in recovery. We do this in a
         * separate pass to allow the kernel to perform all the flushes
         * (especially the metadata ones) at once.
         */
        dbspace_dir = AllocateDir(dbspacedirname);
        while ((de = ReadDir(dbspace_dir, dbspacedirname)) != NULL)
        {
            ForkNumber  forkNum;
            int         oidchars;
            char        oidbuf[OIDCHARS + 1];
            char        mainpath[MAXPGPATH];

            /* Skip anything that doesn't look like a relation data file. */
            if (!parse_filename_for_nontemp_relation(de->d_name, &oidchars,
                                                     &forkNum))
                continue;

            /* Also skip it unless this is the init fork. */
            if (forkNum != INIT_FORKNUM)
                continue;

            /* Construct main fork pathname. */
            memcpy(oidbuf, de->d_name, oidchars);
            oidbuf[oidchars] = '\0';
            snprintf(mainpath, sizeof(mainpath), "%s/%s%s",
                     dbspacedirname, oidbuf, de->d_name + oidchars + 1 +
                     strlen(forkNames[INIT_FORKNUM]));

            fsync_fname(mainpath, false);
        }

        FreeDir(dbspace_dir);

        /*
         * Lastly, fsync the database directory itself, ensuring the
         * filesystem remembers the file creations and deletions we've done.
         * We don't bother with this during a call that does only
         * UNLOGGED_RELATION_CLEANUP, because if recovery crashes before we
         * get to doing UNLOGGED_RELATION_INIT, we'll redo the cleanup step
         * too at the next startup attempt.
         */
        fsync_fname(dbspacedirname, true);
    }
}

/*
 * Basic parsing of putative relation filenames.
 *
 * This function returns true if the file appears to be in the correct format
 * for a non-temporary relation and false otherwise.
 *
 * NB: If this function returns true, the caller is entitled to assume that
 * *oidchars has been set to the a value no more than OIDCHARS, and thus
 * that a buffer of OIDCHARS+1 characters is sufficient to hold the OID
 * portion of the filename.  This is critical to protect against a possible
 * buffer overrun.
 */
bool
parse_filename_for_nontemp_relation(const char *name, int *oidchars,
                                    ForkNumber *fork)
{
    int         pos;

    /* Look for a non-empty string of digits (that isn't too long). */
    for (pos = 0; isdigit((unsigned char) name[pos]); ++pos)
        ;
    if (pos == 0 || pos > OIDCHARS)
        return false;
    *oidchars = pos;

    /* Check for a fork name. */
    if (name[pos] != '_')
        *fork = MAIN_FORKNUM;
    else
    {
        int         forkchar;

        forkchar = forkname_chars(&name[pos + 1], fork);
        if (forkchar <= 0)
            return false;
        pos += forkchar + 1;
    }

    /* Check for a segment number. */
    if (name[pos] == '.')
    {
        int         segchar;

        for (segchar = 1; isdigit((unsigned char) name[pos + segchar]); ++segchar)
            ;
        if (segchar <= 1)
            return false;
        pos += segchar;
    }

    /* Now we should be at the end. */
    if (name[pos] != '\0')
        return false;
    return true;
}