src/bin/pg_basebackup/walmethods.h

   1 /*-------------------------------------------------------------------------
   2  *
   3  * walmethods.h
   4  *
   5  * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
   6  *
   7  * IDENTIFICATION
   8  *                src/bin/pg_basebackup/walmethods.h
   9  *-------------------------------------------------------------------------
  10  */
  11
  12
  13 typedef void *Walfile;
  14
  15 typedef enum
  16 {
  17         CLOSE_NORMAL,
  18         CLOSE_UNLINK,
  19         CLOSE_NO_RENAME
  20 } WalCloseMethod;
  21
  22 /*
  23  * A WalWriteMethod structure represents the different methods used
  24  * to write the streaming WAL as it's received.
  25  *
  26  * All methods that have a failure return indicator will set state
  27  * allowing the getlasterror() method to return a suitable message.
  28  * Commonly, errno is this state (or part of it); so callers must take
  29  * care not to clobber errno between a failed method call and use of
  30  * getlasterror() to retrieve the message.
  31  */
  32 typedef struct WalWriteMethod WalWriteMethod;
  33 struct WalWriteMethod
  34 {
  35         /*
  36          * Open a target file. Returns Walfile, or NULL if open failed. If a temp
  37          * suffix is specified, a file with that name will be opened, and then
  38          * automatically renamed in close(). If pad_to_size is specified, the file
  39          * will be padded with NUL up to that size, if supported by the Walmethod.
  40          */
  41         Walfile         (*open_for_write) (const char *pathname, const char *temp_suffix, size_t pad_to_size);
  42
  43         /*
  44          * Close an open Walfile, using one or more methods for handling automatic
  45          * unlinking etc. Returns 0 on success, other values for error.
  46          */
  47         int                     (*close) (Walfile f, WalCloseMethod method);
  48
  49         /* Check if a file exist */
  50         bool            (*existsfile) (const char *pathname);
  51
  52         /* Return the size of a file, or -1 on failure. */
  53         ssize_t         (*get_file_size) (const char *pathname);
  54
  55         /*
  56          * Return the name of the current file to work on in pg_malloc()'d string,
  57          * without the base directory.  This is useful for logging.
  58          */
  59         char       *(*get_file_name) (const char *pathname, const char *temp_suffix);
  60
  61         /* Return the level of compression */
  62         int                     (*compression) (void);
  63
  64         /*
  65          * Write count number of bytes to the file, and return the number of bytes
  66          * actually written or -1 for error.
  67          */
  68         ssize_t         (*write) (Walfile f, const void *buf, size_t count);
  69
  70         /* Return the current position in a file or -1 on error */
  71         off_t           (*get_current_pos) (Walfile f);
  72
  73         /*
  74          * fsync the contents of the specified file. Returns 0 on success.
  75          */
  76         int                     (*sync) (Walfile f);
  77
  78         /*
  79          * Clean up the Walmethod, closing any shared resources. For methods like
  80          * tar, this includes writing updated headers. Returns true if the
  81          * close/write/sync of shared resources succeeded, otherwise returns false
  82          * (but the resources are still closed).
  83          */
  84         bool            (*finish) (void);
  85
  86         /* Return a text for the last error in this Walfile */
  87         const char *(*getlasterror) (void);
  88 };
  89
  90 /*
  91  * Available WAL methods:
  92  *      - WalDirectoryMethod - write WAL to regular files in a standard pg_wal
  93  *      - WalTarMethod       - write WAL to a tarfile corresponding to pg_wal
  94  *                                                 (only implements the methods required for pg_basebackup,
  95  *                                                 not all those required for pg_receivewal)
  96  */
  97 WalWriteMethod *CreateWalDirectoryMethod(const char *basedir,
  98                                                                                  int compression, bool sync);
  99 WalWriteMethod *CreateWalTarMethod(const char *tarbase, int compression, bool sync);
 100
 101 /* Cleanup routines for previously-created methods */
 102 void            FreeWalDirectoryMethod(void);
 103 void            FreeWalTarMethod(void);