*/
/*
-** LOG SUMMARY FORMAT
+** LOG SUMMARY FILE FORMAT
**
-** TODO.
+** The log-summary file consists of a header region, followed by an
+** region that contains no useful data (used to apply byte-range locks
+** to), followed by the data region.
+**
+** The contents of both the header and data region are specified in terms
+** of 1, 2 and 4 byte unsigned integers. All integers are stored in
+** machine-endian order.
+**
+** A log-summary file is essentially a shadow-pager map. It contains a
+** mapping from database page number to the set of locations in the log
+** file that contain versions of the database page. When a database
+** client needs to read a page of data, it first queries the log-summary
+** file to determine if the required version of the page is stored in
+** the log. If so, it is read from the log file. If not, it is read from
+** the database file.
+**
+** Whenever a transaction is appended to the log or a checkpoint transfers
+** data from the log file into the database file, the log-summary is
+** updated accordingly.
+**
+** The fields in the log-summary file header are described in the comment
+** directly above the definition of struct LogSummaryHdr (see below).
+** Immediately following the fields in the LogSummaryHdr structure is
+** an 8 byte checksum based on the contents of the header. This field is
+** not the same as the iCheck1 and iCheck2 fields of the LogSummaryHdr.
*/
#include "log.h"
/* Size of serialized LogSummaryHdr object. */
#define LOGSUMMARY_HDR_NFIELD (sizeof(LogSummaryHdr) / sizeof(u32))
-#define LOGSUMMARY_FRAME_OFFSET \
- (LOGSUMMARY_HDR_NFIELD + LOG_CKSM_BYTES/sizeof(u32))
-
-
+/* A block of 16 bytes beginning at LOGSUMMARY_LOCK_OFFSET is reserved
+** for locks. Since some systems only feature mandatory file-locks, we
+** do not read or write data from the region of the file on which locks
+** are applied.
+*/
+#define LOGSUMMARY_LOCK_OFFSET ((sizeof(LogSummaryHdr))+2*sizeof(u32))
+#define LOGSUMMARY_LOCK_RESERVED 16
-/* Size of frame header */
+/* Size of header before each frame in log file */
#define LOG_FRAME_HDRSIZE 16
-#define LOG_HDRSIZE 12
+
+/* Size of log header */
+#define LOG_HDRSIZE 12
/*
** Return the offset of frame iFrame in the log file, assuming a database
** log frame-header.
*/
#define logFrameOffset(iFrame, pgsz) ( \
- LOG_HDRSIZE + ((iFrame)-1)*((pgsz)+LOG_FRAME_HDRSIZE) \
+ LOG_HDRSIZE + ((iFrame)-1)*((pgsz)+LOG_FRAME_HDRSIZE) \
)
/*
** write to the log file) require an exclusive lock on region D.
** Which they cannot get until all region D readers have finished.
*/
-#define LOG_LOCK_MUTEX 12
-#define LOG_LOCK_DMH 13
-#define LOG_LOCK_REGION 14
+#define LOG_LOCK_MUTEX (LOGSUMMARY_LOCK_OFFSET)
+#define LOG_LOCK_DMH (LOG_LOCK_MUTEX+1)
+#define LOG_LOCK_REGION (LOG_LOCK_DMH+1)
/*
** The four lockable regions associated with each log-summary. A connection
}
static void logSummaryWriteHdr(LogSummary *pSummary, LogSummaryHdr *pHdr){
- u32 *aData = pSummary->aData;
- memcpy(aData, pHdr, sizeof(LogSummaryHdr));
- aData[LOGSUMMARY_HDR_NFIELD] = 1;
- aData[LOGSUMMARY_HDR_NFIELD+1] = 1;
- logChecksumBytes(
- (u8 *)aData, sizeof(LogSummaryHdr), &aData[LOGSUMMARY_HDR_NFIELD]
- );
+ u32 *aHdr = pSummary->aData; /* Write header here */
+ u32 *aCksum = &aHdr[LOGSUMMARY_HDR_NFIELD]; /* Write header cksum here */
+
+ assert( LOGSUMMARY_HDR_NFIELD==sizeof(LogSummaryHdr)/4 );
+ memcpy(aHdr, pHdr, sizeof(LogSummaryHdr));
+ aCksum[0] = aCksum[1] = 1;
+ logChecksumBytes((u8 *)aHdr, sizeof(LogSummaryHdr), aCksum);
}
/*
** alternating "map" and "index" blocks.
*/
static int logSummaryEntry(u32 iFrame){
- return ((((iFrame-1)>>8)<<6) + iFrame-1 + 2 + LOGSUMMARY_HDR_NFIELD);
+ return (
+ (LOGSUMMARY_LOCK_OFFSET+LOGSUMMARY_LOCK_RESERVED)/sizeof(u32)
+ + (((iFrame-1)>>8)<<6) /* Indexes that occur before iFrame */
+ + iFrame-1 /* Db page numbers that occur before iFrame */
+ );
}
/*
** Place, modify or remove a lock on the log-summary file associated
** with pSummary.
+**
+** The locked byte-range should be inside the region dedicated to
+** locking. This region of the log-summary file is never read or written.
*/
static int logLockFd(
LogSummary *pSummary, /* The log-summary object to lock */
assert( ArraySize(aType)==ArraySize(aOp) );
assert( op>=0 && op<ArraySize(aType) );
+ assert( nByte>0 );
+ assert( iStart>=LOGSUMMARY_LOCK_OFFSET
+ && iStart+nByte<=LOGSUMMARY_LOCK_OFFSET+LOGSUMMARY_LOCK_RESERVED
+ );
+#if defined(SQLITE_DEBUG) && defined(SQLITE_OS_UNIX)
+ if( pSummary->aData ) memset(&((u8*)pSummary->aData)[iStart], op, nByte);
+#endif
memset(&f, 0, sizeof(f));
f.l_type = aType[op];
int iStart; /* Byte offset to start locking operation */
int iLen; /* Length field for locking operation */
} aMap[] = {
- /* 0000 */ {0, 0}, /* 0001 */ {4+LOG_LOCK_REGION, 1},
- /* 0010 */ {3+LOG_LOCK_REGION, 1}, /* 0011 */ {3+LOG_LOCK_REGION, 2},
- /* 0100 */ {2+LOG_LOCK_REGION, 1}, /* 0101 */ {0, 0},
- /* 0110 */ {2+LOG_LOCK_REGION, 2}, /* 0111 */ {2+LOG_LOCK_REGION, 3},
- /* 1000 */ {1+LOG_LOCK_REGION, 1}, /* 1001 */ {0, 0},
+ /* 0000 */ {0, 0}, /* 0001 */ {3+LOG_LOCK_REGION, 1},
+ /* 0010 */ {2+LOG_LOCK_REGION, 1}, /* 0011 */ {2+LOG_LOCK_REGION, 2},
+ /* 0100 */ {1+LOG_LOCK_REGION, 1}, /* 0101 */ {0, 0},
+ /* 0110 */ {1+LOG_LOCK_REGION, 2}, /* 0111 */ {1+LOG_LOCK_REGION, 3},
+ /* 1000 */ {0+LOG_LOCK_REGION, 1}, /* 1001 */ {0, 0},
/* 1010 */ {0, 0}, /* 1011 */ {0, 0},
- /* 1100 */ {1+LOG_LOCK_REGION, 2}, /* 1101 */ {0, 0},
+ /* 1100 */ {0+LOG_LOCK_REGION, 2}, /* 1101 */ {0, 0},
/* 1110 */ {0, 0}, /* 1111 */ {0, 0}
};
int rc; /* Return code of logLockFd() */
projects / thirdparty / sqlite.git / commitdiff
