diff options
Diffstat (limited to 'src')
| -rw-r--r-- | src/log.c | 95 |
1 files changed, 69 insertions, 26 deletions
@@ -28,9 +28,33 @@ */ /* -** 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" @@ -65,14 +89,19 @@ struct LogSummaryHdr { /* 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 @@ -80,7 +109,7 @@ struct LogSummaryHdr { ** log frame-header. */ #define logFrameOffset(iFrame, pgsz) ( \ - LOG_HDRSIZE + ((iFrame)-1)*((pgsz)+LOG_FRAME_HDRSIZE) \ + LOG_HDRSIZE + ((iFrame)-1)*((pgsz)+LOG_FRAME_HDRSIZE) \ ) /* @@ -197,9 +226,9 @@ struct LogSummary { ** 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 @@ -386,13 +415,13 @@ static int logSummaryUnmap(LogSummary *pSummary, int isUnlink){ } 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); } /* @@ -553,7 +582,11 @@ static int logSummaryMap(LogSummary *pSummary, int nByte){ ** 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 */ + ); } @@ -692,6 +725,9 @@ finished: /* ** 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 */ @@ -716,6 +752,13 @@ static int logLockFd( 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]; @@ -834,13 +877,13 @@ static int logLockRegion(Log *pLog, u32 mRegion, int 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() */ |