/*------------------------------------------------------------------------- * * xlogreader.h * Definitions for the generic XLog reading facility * * Portions Copyright (c) 2013-2020, PostgreSQL Global Development Group * * IDENTIFICATION * src/include/access/xlogreader.h * * NOTES * See the definition of the XLogReaderState struct for instructions on * how to use the XLogReader infrastructure. * * The basic idea is to allocate an XLogReaderState via * XLogReaderAllocate(), position the reader to the first record with * XLogBeginRead() or XLogFindNextRecord(), and call XLogReadRecord() * until it returns NULL. * * After reading a record with XLogReadRecord(), it's decomposed into * the per-block and main data parts, and the parts can be accessed * with the XLogRec* macros and functions. You can also decode a * record that's already constructed in memory, without reading from * disk, by calling the DecodeXLogRecord() function. *------------------------------------------------------------------------- */ #ifndef XLOGREADER_H #define XLOGREADER_H #ifndef FRONTEND #include "access/transam.h" #endif #include "access/xlogrecord.h" /* WALOpenSegment represents a WAL segment being read. */ typedef struct WALOpenSegment { int ws_file; /* segment file descriptor */ XLogSegNo ws_segno; /* segment number */ TimeLineID ws_tli; /* timeline ID of the currently open file */ } WALOpenSegment; /* WALSegmentContext carries context information about WAL segments to read */ typedef struct WALSegmentContext { char ws_dir[MAXPGPATH]; int ws_segsize; } WALSegmentContext; typedef struct XLogReaderState XLogReaderState; /* Function type definition for the read_page callback */ typedef int (*XLogPageReadCB) (XLogReaderState *xlogreader, XLogRecPtr targetPagePtr, int reqLen, XLogRecPtr targetRecPtr, char *readBuf); typedef struct { /* Is this block ref in use? */ bool in_use; /* Identify the block this refers to */ RelFileNode rnode; ForkNumber forknum; BlockNumber blkno; /* copy of the fork_flags field from the XLogRecordBlockHeader */ uint8 flags; /* Information on full-page image, if any */ bool has_image; /* has image, even for consistency checking */ bool apply_image; /* has image that should be restored */ char *bkp_image; uint16 hole_offset; uint16 hole_length; uint16 bimg_len; uint8 bimg_info; /* Buffer holding the rmgr-specific data associated with this block */ bool has_data; char *data; uint16 data_len; uint16 data_bufsz; } DecodedBkpBlock; struct XLogReaderState { /* ---------------------------------------- * Public parameters * ---------------------------------------- */ /* * Data input callback (mandatory). * * This callback shall read at least reqLen valid bytes of the xlog page * starting at targetPagePtr, and store them in readBuf. The callback * shall return the number of bytes read (never more than XLOG_BLCKSZ), or * -1 on failure. The callback shall sleep, if necessary, to wait for the * requested bytes to become available. The callback will not be invoked * again for the same page unless more than the returned number of bytes * are needed. * * targetRecPtr is the position of the WAL record we're reading. Usually * it is equal to targetPagePtr + reqLen, but sometimes xlogreader needs * to read and verify the page or segment header, before it reads the * actual WAL record it's interested in. In that case, targetRecPtr can * be used to determine which timeline to read the page from. * * The callback shall set ->seg.ws_tli to the TLI of the file the page was * read from. */ XLogPageReadCB read_page; /* * System identifier of the xlog files we're about to read. Set to zero * (the default value) if unknown or unimportant. */ uint64 system_identifier; /* * Opaque data for callbacks to use. Not used by XLogReader. */ void *private_data; /* * Start and end point of last record read. EndRecPtr is also used as the * position to read next. Calling XLogBeginRead() sets EndRecPtr to the * starting position and ReadRecPtr to invalid. */ XLogRecPtr ReadRecPtr; /* start of last record read */ XLogRecPtr EndRecPtr; /* end+1 of last record read */ /* ---------------------------------------- * Decoded representation of current record * * Use XLogRecGet* functions to investigate the record; these fields * should not be accessed directly. * ---------------------------------------- */ XLogRecord *decoded_record; /* currently decoded record */ char *main_data; /* record's main data portion */ uint32 main_data_len; /* main data portion's length */ uint32 main_data_bufsz; /* allocated size of the buffer */ RepOriginId record_origin; /* information about blocks referenced by the record. */ DecodedBkpBlock blocks[XLR_MAX_BLOCK_ID + 1]; int max_block_id; /* highest block_id in use (-1 if none) */ /* ---------------------------------------- * private/internal state * ---------------------------------------- */ /* * Buffer for currently read page (XLOG_BLCKSZ bytes, valid up to at least * readLen bytes) */ char *readBuf; uint32 readLen; /* last read XLOG position for data currently in readBuf */ WALSegmentContext segcxt; WALOpenSegment seg; uint32 segoff; /* * beginning of prior page read, and its TLI. Doesn't necessarily * correspond to what's in readBuf; used for timeline sanity checks. */ XLogRecPtr latestPagePtr; TimeLineID latestPageTLI; /* beginning of the WAL record being read. */ XLogRecPtr currRecPtr; /* timeline to read it from, 0 if a lookup is required */ TimeLineID currTLI; /* * Safe point to read to in currTLI if current TLI is historical * (tliSwitchPoint) or InvalidXLogRecPtr if on current timeline. * * Actually set to the start of the segment containing the timeline switch * that ends currTLI's validity, not the LSN of the switch its self, since * we can't assume the old segment will be present. */ XLogRecPtr currTLIValidUntil; /* * If currTLI is not the most recent known timeline, the next timeline to * read from when currTLIValidUntil is reached. */ TimeLineID nextTLI; /* * Buffer for current ReadRecord result (expandable), used when a record * crosses a page boundary. */ char *readRecordBuf; uint32 readRecordBufSize; /* Buffer to hold error message */ char *errormsg_buf; }; /* Get a new XLogReader */ extern XLogReaderState *XLogReaderAllocate(int wal_segment_size, const char *waldir, XLogPageReadCB pagereadfunc, void *private_data); /* Free an XLogReader */ extern void XLogReaderFree(XLogReaderState *state); /* * Callback to open the specified WAL segment for reading. Returns a valid * file descriptor when the file was opened successfully. * * "nextSegNo" is the number of the segment to be opened. * * "segcxt" is additional information about the segment. * * "tli_p" is an input/output argument. XLogRead() uses it to pass the * timeline in which the new segment should be found, but the callback can use * it to return the TLI that it actually opened. * * BasicOpenFile() is the preferred way to open the segment file in backend * code, whereas open(2) should be used in frontend. */ typedef int (*WALSegmentOpen) (XLogSegNo nextSegNo, WALSegmentContext *segcxt, TimeLineID *tli_p); /* Initialize supporting structures */ extern void WALOpenSegmentInit(WALOpenSegment *seg, WALSegmentContext *segcxt, int segsize, const char *waldir); /* Position the XLogReader to given record */ extern void XLogBeginRead(XLogReaderState *state, XLogRecPtr RecPtr); #ifdef FRONTEND extern XLogRecPtr XLogFindNextRecord(XLogReaderState *state, XLogRecPtr RecPtr); #endif /* FRONTEND */ /* Read the next XLog record. Returns NULL on end-of-WAL or failure */ extern struct XLogRecord *XLogReadRecord(XLogReaderState *state, char **errormsg); /* Validate a page */ extern bool XLogReaderValidatePageHeader(XLogReaderState *state, XLogRecPtr recptr, char *phdr); /* * Error information from WALRead that both backend and frontend caller can * process. Currently only errors from pg_pread can be reported. */ typedef struct WALReadError { int wre_errno; /* errno set by the last pg_pread() */ int wre_off; /* Offset we tried to read from. */ int wre_req; /* Bytes requested to be read. */ int wre_read; /* Bytes read by the last read(). */ WALOpenSegment wre_seg; /* Segment we tried to read from. */ } WALReadError; extern bool WALRead(char *buf, XLogRecPtr startptr, Size count, TimeLineID tli, WALOpenSegment *seg, WALSegmentContext *segcxt, WALSegmentOpen openSegment, WALReadError *errinfo); /* Functions for decoding an XLogRecord */ extern bool DecodeXLogRecord(XLogReaderState *state, XLogRecord *record, char **errmsg); #define XLogRecGetTotalLen(decoder) ((decoder)->decoded_record->xl_tot_len) #define XLogRecGetPrev(decoder) ((decoder)->decoded_record->xl_prev) #define XLogRecGetInfo(decoder) ((decoder)->decoded_record->xl_info) #define XLogRecGetRmid(decoder) ((decoder)->decoded_record->xl_rmid) #define XLogRecGetXid(decoder) ((decoder)->decoded_record->xl_xid) #define XLogRecGetOrigin(decoder) ((decoder)->record_origin) #define XLogRecGetData(decoder) ((decoder)->main_data) #define XLogRecGetDataLen(decoder) ((decoder)->main_data_len) #define XLogRecHasAnyBlockRefs(decoder) ((decoder)->max_block_id >= 0) #define XLogRecHasBlockRef(decoder, block_id) \ ((decoder)->blocks[block_id].in_use) #define XLogRecHasBlockImage(decoder, block_id) \ ((decoder)->blocks[block_id].has_image) #define XLogRecBlockImageApply(decoder, block_id) \ ((decoder)->blocks[block_id].apply_image) #ifndef FRONTEND extern FullTransactionId XLogRecGetFullXid(XLogReaderState *record); #endif extern bool RestoreBlockImage(XLogReaderState *record, uint8 block_id, char *page); extern char *XLogRecGetBlockData(XLogReaderState *record, uint8 block_id, Size *len); extern bool XLogRecGetBlockTag(XLogReaderState *record, uint8 block_id, RelFileNode *rnode, ForkNumber *forknum, BlockNumber *blknum); #endif /* XLOGREADER_H */