341 lines
11 KiB
C
341 lines
11 KiB
C
/*-------------------------------------------------------------------------
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*
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* xlogreader.h
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* Definitions for the generic XLog reading facility
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*
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* Portions Copyright (c) 2013-2021, PostgreSQL Global Development Group
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*
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* IDENTIFICATION
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* src/include/access/xlogreader.h
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*
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* NOTES
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* See the definition of the XLogReaderState struct for instructions on
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* how to use the XLogReader infrastructure.
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*
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* The basic idea is to allocate an XLogReaderState via
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* XLogReaderAllocate(), position the reader to the first record with
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* XLogBeginRead() or XLogFindNextRecord(), and call XLogReadRecord()
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* until it returns NULL.
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*
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* Callers supply a page_read callback if they want to call
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* XLogReadRecord or XLogFindNextRecord; it can be passed in as NULL
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* otherwise. The WALRead function can be used as a helper to write
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* page_read callbacks, but it is not mandatory; callers that use it,
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* must supply segment_open callbacks. The segment_close callback
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* must always be supplied.
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*
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* After reading a record with XLogReadRecord(), it's decomposed into
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* the per-block and main data parts, and the parts can be accessed
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* with the XLogRec* macros and functions. You can also decode a
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* record that's already constructed in memory, without reading from
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* disk, by calling the DecodeXLogRecord() function.
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*-------------------------------------------------------------------------
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*/
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#ifndef XLOGREADER_H
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#define XLOGREADER_H
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#ifndef FRONTEND
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#include "access/transam.h"
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#endif
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#include "access/xlogrecord.h"
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/* WALOpenSegment represents a WAL segment being read. */
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typedef struct WALOpenSegment
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{
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int ws_file; /* segment file descriptor */
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XLogSegNo ws_segno; /* segment number */
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TimeLineID ws_tli; /* timeline ID of the currently open file */
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} WALOpenSegment;
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/* WALSegmentContext carries context information about WAL segments to read */
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typedef struct WALSegmentContext
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{
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char ws_dir[MAXPGPATH];
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int ws_segsize;
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} WALSegmentContext;
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typedef struct XLogReaderState XLogReaderState;
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/* Function type definitions for various xlogreader interactions */
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typedef int (*XLogPageReadCB) (XLogReaderState *xlogreader,
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XLogRecPtr targetPagePtr,
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int reqLen,
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XLogRecPtr targetRecPtr,
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char *readBuf);
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typedef void (*WALSegmentOpenCB) (XLogReaderState *xlogreader,
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XLogSegNo nextSegNo,
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TimeLineID *tli_p);
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typedef void (*WALSegmentCloseCB) (XLogReaderState *xlogreader);
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typedef struct XLogReaderRoutine
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{
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/*
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* Data input callback
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*
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* This callback shall read at least reqLen valid bytes of the xlog page
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* starting at targetPagePtr, and store them in readBuf. The callback
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* shall return the number of bytes read (never more than XLOG_BLCKSZ), or
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* -1 on failure. The callback shall sleep, if necessary, to wait for the
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* requested bytes to become available. The callback will not be invoked
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* again for the same page unless more than the returned number of bytes
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* are needed.
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*
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* targetRecPtr is the position of the WAL record we're reading. Usually
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* it is equal to targetPagePtr + reqLen, but sometimes xlogreader needs
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* to read and verify the page or segment header, before it reads the
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* actual WAL record it's interested in. In that case, targetRecPtr can
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* be used to determine which timeline to read the page from.
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*
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* The callback shall set ->seg.ws_tli to the TLI of the file the page was
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* read from.
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*/
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XLogPageReadCB page_read;
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/*
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* Callback to open the specified WAL segment for reading. ->seg.ws_file
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* shall be set to the file descriptor of the opened segment. In case of
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* failure, an error shall be raised by the callback and it shall not
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* return.
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*
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* "nextSegNo" is the number of the segment to be opened.
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*
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* "tli_p" is an input/output argument. WALRead() uses it to pass the
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* timeline in which the new segment should be found, but the callback can
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* use it to return the TLI that it actually opened.
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*/
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WALSegmentOpenCB segment_open;
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/*
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* WAL segment close callback. ->seg.ws_file shall be set to a negative
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* number.
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*/
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WALSegmentCloseCB segment_close;
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} XLogReaderRoutine;
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#define XL_ROUTINE(...) &(XLogReaderRoutine){__VA_ARGS__}
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typedef struct
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{
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/* Is this block ref in use? */
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bool in_use;
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/* Identify the block this refers to */
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RelFileNode rnode;
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ForkNumber forknum;
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BlockNumber blkno;
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/* copy of the fork_flags field from the XLogRecordBlockHeader */
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uint8 flags;
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/* Information on full-page image, if any */
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bool has_image; /* has image, even for consistency checking */
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bool apply_image; /* has image that should be restored */
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char *bkp_image;
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uint16 hole_offset;
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uint16 hole_length;
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uint16 bimg_len;
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uint8 bimg_info;
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/* Buffer holding the rmgr-specific data associated with this block */
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bool has_data;
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char *data;
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uint16 data_len;
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uint16 data_bufsz;
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} DecodedBkpBlock;
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struct XLogReaderState
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{
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/*
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* Operational callbacks
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*/
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XLogReaderRoutine routine;
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/* ----------------------------------------
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* Public parameters
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* ----------------------------------------
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*/
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/*
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* System identifier of the xlog files we're about to read. Set to zero
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* (the default value) if unknown or unimportant.
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*/
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uint64 system_identifier;
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/*
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* Opaque data for callbacks to use. Not used by XLogReader.
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*/
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void *private_data;
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/*
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* Start and end point of last record read. EndRecPtr is also used as the
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* position to read next. Calling XLogBeginRead() sets EndRecPtr to the
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* starting position and ReadRecPtr to invalid.
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*/
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XLogRecPtr ReadRecPtr; /* start of last record read */
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XLogRecPtr EndRecPtr; /* end+1 of last record read */
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/* ----------------------------------------
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* Decoded representation of current record
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*
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* Use XLogRecGet* functions to investigate the record; these fields
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* should not be accessed directly.
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* ----------------------------------------
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*/
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XLogRecord *decoded_record; /* currently decoded record */
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char *main_data; /* record's main data portion */
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uint32 main_data_len; /* main data portion's length */
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uint32 main_data_bufsz; /* allocated size of the buffer */
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RepOriginId record_origin;
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TransactionId toplevel_xid; /* XID of top-level transaction */
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/* information about blocks referenced by the record. */
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DecodedBkpBlock blocks[XLR_MAX_BLOCK_ID + 1];
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int max_block_id; /* highest block_id in use (-1 if none) */
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/* ----------------------------------------
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* private/internal state
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* ----------------------------------------
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*/
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/*
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* Buffer for currently read page (XLOG_BLCKSZ bytes, valid up to at least
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* readLen bytes)
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*/
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char *readBuf;
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uint32 readLen;
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/* last read XLOG position for data currently in readBuf */
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WALSegmentContext segcxt;
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WALOpenSegment seg;
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uint32 segoff;
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/*
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* beginning of prior page read, and its TLI. Doesn't necessarily
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* correspond to what's in readBuf; used for timeline sanity checks.
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*/
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XLogRecPtr latestPagePtr;
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TimeLineID latestPageTLI;
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/* beginning of the WAL record being read. */
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XLogRecPtr currRecPtr;
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/* timeline to read it from, 0 if a lookup is required */
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TimeLineID currTLI;
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/*
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* Safe point to read to in currTLI if current TLI is historical
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* (tliSwitchPoint) or InvalidXLogRecPtr if on current timeline.
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*
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* Actually set to the start of the segment containing the timeline switch
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* that ends currTLI's validity, not the LSN of the switch its self, since
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* we can't assume the old segment will be present.
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*/
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XLogRecPtr currTLIValidUntil;
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/*
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* If currTLI is not the most recent known timeline, the next timeline to
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* read from when currTLIValidUntil is reached.
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*/
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TimeLineID nextTLI;
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/*
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* Buffer for current ReadRecord result (expandable), used when a record
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* crosses a page boundary.
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*/
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char *readRecordBuf;
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uint32 readRecordBufSize;
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/* Buffer to hold error message */
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char *errormsg_buf;
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/*
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* Set at the end of recovery: the start point of a partial record at the
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* end of WAL (InvalidXLogRecPtr if there wasn't one), and the start
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* location of its first contrecord that went missing.
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*/
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XLogRecPtr abortedRecPtr;
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XLogRecPtr missingContrecPtr;
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/* Set when XLP_FIRST_IS_OVERWRITE_CONTRECORD is found */
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XLogRecPtr overwrittenRecPtr;
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};
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/* Get a new XLogReader */
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extern XLogReaderState *XLogReaderAllocate(int wal_segment_size,
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const char *waldir,
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XLogReaderRoutine *routine,
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void *private_data);
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extern XLogReaderRoutine *LocalXLogReaderRoutine(void);
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/* Free an XLogReader */
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extern void XLogReaderFree(XLogReaderState *state);
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/* Position the XLogReader to given record */
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extern void XLogBeginRead(XLogReaderState *state, XLogRecPtr RecPtr);
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#ifdef FRONTEND
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extern XLogRecPtr XLogFindNextRecord(XLogReaderState *state, XLogRecPtr RecPtr);
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#endif /* FRONTEND */
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/* Read the next XLog record. Returns NULL on end-of-WAL or failure */
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extern struct XLogRecord *XLogReadRecord(XLogReaderState *state,
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char **errormsg);
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/* Validate a page */
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extern bool XLogReaderValidatePageHeader(XLogReaderState *state,
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XLogRecPtr recptr, char *phdr);
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/*
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* Error information from WALRead that both backend and frontend caller can
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* process. Currently only errors from pg_pread can be reported.
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*/
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typedef struct WALReadError
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{
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int wre_errno; /* errno set by the last pg_pread() */
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int wre_off; /* Offset we tried to read from. */
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int wre_req; /* Bytes requested to be read. */
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int wre_read; /* Bytes read by the last read(). */
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WALOpenSegment wre_seg; /* Segment we tried to read from. */
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} WALReadError;
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extern bool WALRead(XLogReaderState *state,
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char *buf, XLogRecPtr startptr, Size count,
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TimeLineID tli, WALReadError *errinfo);
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/* Functions for decoding an XLogRecord */
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extern bool DecodeXLogRecord(XLogReaderState *state, XLogRecord *record,
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char **errmsg);
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#define XLogRecGetTotalLen(decoder) ((decoder)->decoded_record->xl_tot_len)
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#define XLogRecGetPrev(decoder) ((decoder)->decoded_record->xl_prev)
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#define XLogRecGetInfo(decoder) ((decoder)->decoded_record->xl_info)
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#define XLogRecGetRmid(decoder) ((decoder)->decoded_record->xl_rmid)
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#define XLogRecGetXid(decoder) ((decoder)->decoded_record->xl_xid)
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#define XLogRecGetOrigin(decoder) ((decoder)->record_origin)
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#define XLogRecGetTopXid(decoder) ((decoder)->toplevel_xid)
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#define XLogRecGetData(decoder) ((decoder)->main_data)
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#define XLogRecGetDataLen(decoder) ((decoder)->main_data_len)
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#define XLogRecHasAnyBlockRefs(decoder) ((decoder)->max_block_id >= 0)
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#define XLogRecHasBlockRef(decoder, block_id) \
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((decoder)->blocks[block_id].in_use)
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#define XLogRecHasBlockImage(decoder, block_id) \
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((decoder)->blocks[block_id].has_image)
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#define XLogRecBlockImageApply(decoder, block_id) \
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((decoder)->blocks[block_id].apply_image)
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#ifndef FRONTEND
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extern FullTransactionId XLogRecGetFullXid(XLogReaderState *record);
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#endif
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extern bool RestoreBlockImage(XLogReaderState *record, uint8 block_id, char *page);
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extern char *XLogRecGetBlockData(XLogReaderState *record, uint8 block_id, Size *len);
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extern bool XLogRecGetBlockTag(XLogReaderState *record, uint8 block_id,
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RelFileNode *rnode, ForkNumber *forknum,
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BlockNumber *blknum);
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#endif /* XLOGREADER_H */
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