# DB->sync

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    #include <db.h>

    int
    DB->sync(DB *db, u_int32_t flags);

# Description

The DB->sync function flushes any cached information to disk.

If the database is in memory only, the DB->sync function has no effect and will always succeed.

The flags parameter is currently unused, and must be set to 0.

It is important to understand that flushing cached information to disk only minimizes the window of opportunity for corrupted data. Although unlikely, it is possible for database corruption to happen if a system or application crash occurs while writing data to the database. To ensure that database corruption never occurs, applications must either: use transactions and logging with automatic recovery; use logging and application-specific recovery; or edit a copy of the database, and once all applications using the database have successfully called DB->close, atomically replace the original database with the updated copy.

The DB->sync function returns a non-zero error value on failure, 0 on success, and returns DB_INCOMPLETE if the underlying database still has dirty pages in the cache. (The only reason to return DB_INCOMPLETE is if another thread of control was writing pages in the underlying database file at the same time as the DB->sync function was being called. For this reason, a return of DB_INCOMPLETE can normally be ignored; or, in cases where it is a possible return value, there may be no reason to call DB->sync.)

# Errors

The DB->sync function may fail and return a non-zero error for the following conditions:

EINVAL
  An invalid flag value or parameter was specified.

The DB->sync function may fail and return a non-zero error for errors specified for other Berkeley DB and C library or system functions. If a catastrophic error has occurred, the DB->sync function may fail and return DB_RUNRECOVERY, in which case all subsequent Berkeley DB calls will fail in the same way.

# See Also

db_create, DB->associate, DB->close, DB->cursor, DB->del, DB->err, DB->errx DB->fd, DB->get, DB->pget, DB->get_byteswapped, DB->get_type, DB->join, DB->key_range, DB->open, DB->put, DB->remove, DB->rename, DB->set_alloc, DB->set_append_recno, DB->set_bt_compare, DB->set_bt_minkey, DB->set_bt_prefix, DB->set_cachesize, DB->set_dup_compare, DB->set_errcall, DB->set_errfile, DB->set_errpfx, DB->set_feedback, DB->set_flags, DB->set_h_ffactor, DB->set_h_hash, DB->set_h_nelem, DB->set_lorder, DB->set_pagesize, DB->set_paniccall, DB->set_q_extentsize, DB->set_re_delim, DB->set_re_len, DB->set_re_pad, DB->set_re_source, DB->stat, DB->sync, DB->truncate, DB->upgrade, and DB->verify.`

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