1 /*------------------------------------------------------------------------- 2 * 3 * xlogreader.h 4 * Definitions for the generic XLog reading facility 5 * 6 * Portions Copyright (c) 2013-2016, PostgreSQL Global Development Group 7 * 8 * IDENTIFICATION 9 * src/include/access/xlogreader.h 10 * 11 * NOTES 12 * See the definition of the XLogReaderState struct for instructions on 13 * how to use the XLogReader infrastructure. 14 * 15 * The basic idea is to allocate an XLogReaderState via 16 * XLogReaderAllocate(), and call XLogReadRecord() until it returns NULL. 17 * 18 * After reading a record with XLogReadRecord(), it's decomposed into 19 * the per-block and main data parts, and the parts can be accessed 20 * with the XLogRec* macros and functions. You can also decode a 21 * record that's already constructed in memory, without reading from 22 * disk, by calling the DecodeXLogRecord() function. 23 *------------------------------------------------------------------------- 24 */ 25 #ifndef XLOGREADER_H 26 #define XLOGREADER_H 27 28 #include "access/xlogrecord.h" 29 30 typedef struct XLogReaderState XLogReaderState; 31 32 /* Function type definition for the read_page callback */ 33 typedef int (*XLogPageReadCB) (XLogReaderState *xlogreader, 34 XLogRecPtr targetPagePtr, 35 int reqLen, 36 XLogRecPtr targetRecPtr, 37 char *readBuf, 38 TimeLineID *pageTLI); 39 40 typedef struct 41 { 42 /* Is this block ref in use? */ 43 bool in_use; 44 45 /* Identify the block this refers to */ 46 RelFileNode rnode; 47 ForkNumber forknum; 48 BlockNumber blkno; 49 50 /* copy of the fork_flags field from the XLogRecordBlockHeader */ 51 uint8 flags; 52 53 /* Information on full-page image, if any */ 54 bool has_image; 55 char *bkp_image; 56 uint16 hole_offset; 57 uint16 hole_length; 58 uint16 bimg_len; 59 uint8 bimg_info; 60 61 /* Buffer holding the rmgr-specific data associated with this block */ 62 bool has_data; 63 char *data; 64 uint16 data_len; 65 uint16 data_bufsz; 66 } DecodedBkpBlock; 67 68 struct XLogReaderState 69 { 70 /* ---------------------------------------- 71 * Public parameters 72 * ---------------------------------------- 73 */ 74 75 /* 76 * Data input callback (mandatory). 77 * 78 * This callback shall read at least reqLen valid bytes of the xlog page 79 * starting at targetPagePtr, and store them in readBuf. The callback 80 * shall return the number of bytes read (never more than XLOG_BLCKSZ), or 81 * -1 on failure. The callback shall sleep, if necessary, to wait for the 82 * requested bytes to become available. The callback will not be invoked 83 * again for the same page unless more than the returned number of bytes 84 * are needed. 85 * 86 * targetRecPtr is the position of the WAL record we're reading. Usually 87 * it is equal to targetPagePtr + reqLen, but sometimes xlogreader needs 88 * to read and verify the page or segment header, before it reads the 89 * actual WAL record it's interested in. In that case, targetRecPtr can 90 * be used to determine which timeline to read the page from. 91 * 92 * The callback shall set *pageTLI to the TLI of the file the page was 93 * read from. It is currently used only for error reporting purposes, to 94 * reconstruct the name of the WAL file where an error occurred. 95 */ 96 XLogPageReadCB read_page; 97 98 /* 99 * System identifier of the xlog files we're about to read. Set to zero 100 * (the default value) if unknown or unimportant. 101 */ 102 uint64 system_identifier; 103 104 /* 105 * Opaque data for callbacks to use. Not used by XLogReader. 106 */ 107 void *private_data; 108 109 /* 110 * Start and end point of last record read. EndRecPtr is also used as the 111 * position to read next, if XLogReadRecord receives an invalid recptr. 112 */ 113 XLogRecPtr ReadRecPtr; /* start of last record read */ 114 XLogRecPtr EndRecPtr; /* end+1 of last record read */ 115 116 117 /* ---------------------------------------- 118 * Decoded representation of current record 119 * 120 * Use XLogRecGet* functions to investigate the record; these fields 121 * should not be accessed directly. 122 * ---------------------------------------- 123 */ 124 XLogRecord *decoded_record; /* currently decoded record */ 125 126 char *main_data; /* record's main data portion */ 127 uint32 main_data_len; /* main data portion's length */ 128 uint32 main_data_bufsz; /* allocated size of the buffer */ 129 130 RepOriginId record_origin; 131 132 /* information about blocks referenced by the record. */ 133 DecodedBkpBlock blocks[XLR_MAX_BLOCK_ID + 1]; 134 135 int max_block_id; /* highest block_id in use (-1 if none) */ 136 137 /* ---------------------------------------- 138 * private/internal state 139 * ---------------------------------------- 140 */ 141 142 /* 143 * Buffer for currently read page (XLOG_BLCKSZ bytes, valid up to at least 144 * readLen bytes) 145 */ 146 char *readBuf; 147 uint32 readLen; 148 149 /* last read segment, segment offset, TLI for data currently in readBuf */ 150 XLogSegNo readSegNo; 151 uint32 readOff; 152 TimeLineID readPageTLI; 153 154 /* 155 * beginning of prior page read, and its TLI. Doesn't necessarily 156 * correspond to what's in readBuf; used for timeline sanity checks. 157 */ 158 XLogRecPtr latestPagePtr; 159 TimeLineID latestPageTLI; 160 161 /* beginning of the WAL record being read. */ 162 XLogRecPtr currRecPtr; 163 164 /* Buffer for current ReadRecord result (expandable) */ 165 char *readRecordBuf; 166 uint32 readRecordBufSize; 167 168 /* Buffer to hold error message */ 169 char *errormsg_buf; 170 171 /* 172 * Set at the end of recovery: the start point of a partial record at the 173 * end of WAL (InvalidXLogRecPtr if there wasn't one), and the start 174 * location of its first contrecord that went missing. 175 */ 176 XLogRecPtr abortedRecPtr; 177 XLogRecPtr missingContrecPtr; 178 /* Set when XLP_FIRST_IS_OVERWRITE_CONTRECORD is found */ 179 XLogRecPtr overwrittenRecPtr; 180 }; 181 182 /* Get a new XLogReader */ 183 extern XLogReaderState *XLogReaderAllocate(XLogPageReadCB pagereadfunc, 184 void *private_data); 185 186 /* Free an XLogReader */ 187 extern void XLogReaderFree(XLogReaderState *state); 188 189 /* Read the next XLog record. Returns NULL on end-of-WAL or failure */ 190 extern struct XLogRecord *XLogReadRecord(XLogReaderState *state, 191 XLogRecPtr recptr, char **errormsg); 192 193 /* Validate a page */ 194 extern bool XLogReaderValidatePageHeader(XLogReaderState *state, 195 XLogRecPtr recptr, char *phdr); 196 197 /* Invalidate read state */ 198 extern void XLogReaderInvalReadState(XLogReaderState *state); 199 200 #ifdef FRONTEND 201 extern XLogRecPtr XLogFindNextRecord(XLogReaderState *state, XLogRecPtr RecPtr); 202 #endif /* FRONTEND */ 203 204 /* Functions for decoding an XLogRecord */ 205 206 extern bool DecodeXLogRecord(XLogReaderState *state, XLogRecord *record, 207 char **errmsg); 208 209 #define XLogRecGetTotalLen(decoder) ((decoder)->decoded_record->xl_tot_len) 210 #define XLogRecGetPrev(decoder) ((decoder)->decoded_record->xl_prev) 211 #define XLogRecGetInfo(decoder) ((decoder)->decoded_record->xl_info) 212 #define XLogRecGetRmid(decoder) ((decoder)->decoded_record->xl_rmid) 213 #define XLogRecGetXid(decoder) ((decoder)->decoded_record->xl_xid) 214 #define XLogRecGetOrigin(decoder) ((decoder)->record_origin) 215 #define XLogRecGetData(decoder) ((decoder)->main_data) 216 #define XLogRecGetDataLen(decoder) ((decoder)->main_data_len) 217 #define XLogRecHasAnyBlockRefs(decoder) ((decoder)->max_block_id >= 0) 218 #define XLogRecHasBlockRef(decoder, block_id) \ 219 ((decoder)->blocks[block_id].in_use) 220 #define XLogRecHasBlockImage(decoder, block_id) \ 221 ((decoder)->blocks[block_id].has_image) 222 223 extern bool RestoreBlockImage(XLogReaderState *recoder, uint8 block_id, char *dst); 224 extern char *XLogRecGetBlockData(XLogReaderState *record, uint8 block_id, Size *len); 225 extern bool XLogRecGetBlockTag(XLogReaderState *record, uint8 block_id, 226 RelFileNode *rnode, ForkNumber *forknum, 227 BlockNumber *blknum); 228 229 #endif /* XLOGREADER_H */ 230