Interface ISqlJetPager

All Known Implementing Classes:
SqlJetPager

public interface ISqlJetPager
The pages cache subsystem reads and writes a file a page at a time and provides a journal for rollback.
Author:
TMate Software Ltd., Sergey Scherbina (sergey.scherbina@gmail.com)
  • Field Details

    • SQLJET_MIN_SECTOR_SIZE

      static final int SQLJET_MIN_SECTOR_SIZE
      The minimum sector size is 512
    • JOURNAL

      static final String JOURNAL
      See Also:
    • aJournalMagic

      static final ISqlJetMemoryPointer aJournalMagic
      Journal files begin with the following magic string. The data was obtained from /dev/random. It is used only as a sanity check. Since version 2.8.0, the journal format contains additional sanity checking information. If the power fails while the journal is being written, semi-random garbage data might appear in the journal file after power is restored. If an attempt is then made to roll the journal back, the database could be corrupted. The additional sanity checking data is an attempt to discover the garbage in the journal and ignore it. The sanity checking information for the new journal format consists of a 32-bit checksum on each page of data. The checksum covers both the page number and the pPager->pageSize bytes of data for the page. This cksum is initialized to a 32-bit random value that appears in the journal file right after the header. The random initializer is important, because garbage data that appears at the end of a journal is likely data that was once in other files that have now been deleted. If the garbage data came from an obsolete journal file, the checksums might be correct. But by initializing the checksum to random value which is different for every journal, we minimize that risk.
    • PAGER_MAX_PGNO

      static final int PAGER_MAX_PGNO
      The maximum legal page number is (2^31 - 1).
      See Also:
    • SQLJET_DEFAULT_JOURNAL_SIZE_LIMIT

      static final int SQLJET_DEFAULT_JOURNAL_SIZE_LIMIT
      If defined as non-zero, auto-vacuum is enabled by default. Otherwise it must be turned on for each database using "PRAGMA auto_vacuum = 1".
    • MEMORY_DB

      static final String MEMORY_DB
      In-memory database's "file-name".
      See Also:
  • Method Details

    • open

      void open(ISqlJetFileSystem fs, File fileName, Set<SqlJetPagerFlags> flags, SqlJetFileType type, Set<SqlJetFileOpenPermission> permissions) throws SqlJetException
      Open a new page cache. The file to be cached need not exist. The file is not locked until the first call to getPage(int) and is only held open until the last page is released using #unref(ISqlJetPage). If fileName is null then a randomly-named temporary file is created and used as the file to be cached. The file will be deleted automatically when it is closed. If fileName is MEMORY_DB then all information is held in cache. It is never written to disk. This can be used to implement an in-memory database.
      Parameters:
      fs - The file system to use
      fileName - Name of the database file to open
      flags - flags controlling this file
      type - file type passed through to ISqlJetFileSystem.open(java.io.File, SqlJetFileType, Set)
      permissions - permissions passed through to ISqlJetFileSystem.open(java.io.File, SqlJetFileType, Set)
      Throws:
      SqlJetException
    • getFileName

      File getFileName()
      Return the path of the database file.
      Returns:
    • getDirectoryName

      File getDirectoryName()
      Return the directory of the database file.
      Returns:
    • getJournalName

      File getJournalName()
      Return the path of the journal file.
      Returns:
    • getFileSystem

      ISqlJetFileSystem getFileSystem()
      Return the file system for the pager.
      Returns:
    • getFile

      ISqlJetFile getFile()
      Return the file handle for the database file associated with the pager. This might return NULL if the file has not yet been opened.
      Returns:
    • isReadOnly

      boolean isReadOnly()
      Return TRUE if the database file is opened read-only. Return FALSE if the database is (in theory) writable.
      Returns:
    • isNoSync

      boolean isNoSync()
      Return true if fsync() calls are disabled for this pager. Return FALSE if fsync()s are executed normally.
      Returns:
    • getLockingMode

      SqlJetPagerLockingMode getLockingMode()
      Get the locking-mode for this pager.
      Returns:
    • setLockingMode

      void setLockingMode(SqlJetPagerLockingMode lockingMode)
      Set the locking-mode for this pager.
      Parameters:
      lockingMode -
    • getJournalMode

      SqlJetPagerJournalMode getJournalMode()
      Get the journal-mode for this pager.
      Parameters:
      journalMode -
      Returns:
    • setJournalMode

      void setJournalMode(SqlJetPagerJournalMode journalMode)
      Set the journal-mode for this pager.
      Parameters:
      journalMode -
    • getJournalSizeLimit

      long getJournalSizeLimit()
      Get the size-limit used for persistent journal files.
      Returns:
    • setJournalSizeLimit

      void setJournalSizeLimit(long limit)
      Set the size-limit used for persistent journal files.
      Parameters:
      limit -
    • setSafetyLevel

      void setSafetyLevel(SqlJetSafetyLevel safetyLevel)
      Set safety level
      Parameters:
      safetyLevel -
    • getSafetyLevel

      SqlJetSafetyLevel getSafetyLevel()
      Get safety level
      Returns:
    • getTempSpace

      ISqlJetMemoryPointer getTempSpace()
      Return a pointer to the "temporary page" buffer held internally by the pager. This is a buffer that is big enough to hold the entire content of a database page. This buffer is used internally during rollback and will be overwritten whenever a rollback occurs. But other modules are free to use it too, as long as no rollbacks are happening.
      Returns:
    • setBusyhandler

      void setBusyhandler(ISqlJetBusyHandler busyHandler)
      Set the busy handler function.
      Parameters:
      busyHandler -
    • setReiniter

      void setReiniter(ISqlJetPageCallback reinitier)
      Set the reinitializer for this pager. If not NULL, the reinitializer is called when the content of a page in cache is restored to its original value as a result of a rollback. The callback gives higher-level code an opportunity to restore the EXTRA section to agree with the restored page data.
      Parameters:
      reinitier -
    • setPageSize

      int setPageSize(int pageSize) throws SqlJetException
      Set the page size to pageSize. If the suggest new page size is inappropriate, then an alternative page size is set to that value before returning.
      Parameters:
      pageSize -
      Returns:
      Throws:
      SqlJetException
    • getPageSize

      int getPageSize()
      Get the page size.
      Returns:
    • setMaxPageCount

      void setMaxPageCount(int maxPageCount) throws SqlJetException
      Attempt to set the maximum database page count if mxPage is positive. Make no changes if mxPage is zero or negative. And never reduce the maximum page count below the current size of the database.
      Parameters:
      maxPageCount -
      Throws:
      SqlJetException
    • getMaxPageCount

      int getMaxPageCount()
      Return the current maximum page count.
      Returns:
    • setCacheSize

      void setCacheSize(int cacheSize)
      Change the maximum number of in-memory pages that are allowed.
      Parameters:
      cacheSize -
    • readFileHeader

      void readFileHeader(int count, ISqlJetMemoryPointer buffer) throws SqlJetIOException
      Read the first N bytes from the beginning of the file into memory that buffer points to. No error checking is done. The rational for this is that this function may be called even if the file does not exist or contain a header. In these cases sqlite3OsRead() will return an error, to which the correct response is to zero the memory at pDest and continue. A real IO error will presumably recur and be picked up later (Todo: Think about this).
      Parameters:
      count -
      buffer -
      Throws:
      SqlJetIOException
    • getPageCount

      int getPageCount() throws SqlJetException
      Return the total number of pages in the disk file associated with pager. If the PENDING_BYTE lies on the page directly after the end of the file, then consider this page part of the file too. For example, if PENDING_BYTE is byte 4096 (the first byte of page 5) and the size of the file is 4096 bytes, 5 is returned instead of 4.
      Returns:
      pages count
      Throws:
      SqlJetException - if pager is in error state.
    • close

      void close() throws SqlJetException
      Shutdown the page cache. Free all memory and close all files. If a transaction was in progress when this routine is called, that transaction is rolled back. All outstanding pages are invalidated and their memory is freed. Any attempt to use a page associated with this page cache after this function returns will likely result in a coredump. This function always succeeds. If a transaction is active an attempt is made to roll it back. If an error occurs during the rollback a hot journal may be left in the filesystem but no error is returned to the caller.
      Throws:
      SqlJetException
    • acquirePage

      ISqlJetPage acquirePage(int pageNumber, boolean read) throws SqlJetException
      Acquire a page. A read lock on the disk file is obtained when the first page is acquired. This read lock is dropped when the last page is released. This routine works for any page number greater than 0. If the database file is smaller than the requested page, then no actual disk read occurs and the memory image of the page is initialized to all zeros. The extra data appended to a page is always initialized to zeros the first time a page is loaded into memory. The acquisition might fail for several reasons. In all cases, an appropriate error code is returned and *ppPage is set to NULL. See also lookupPage(int). Both this routine and lookupPage(int) attempt to find a page in the in-memory cache first. If the page is not already in memory, this routine goes to disk to read it in whereas lookupPage(int) just returns 0. This routine acquires a read-lock the first time it has to go to disk, and could also playback an old journal if necessary. Since lookupPage(int) never goes to disk, it never has to deal with locks or journal files. If noContent is false, the page contents are actually read from disk. If noContent is true, it means that we do not care about the contents of the page at this time, so do not do a disk read. Just fill in the page content with zeros. But mark the fact that we have not read the content by setting the PgHdr.needRead flag. Later on, if sqlite3PagerWrite() is called on this page or if this routine is called again with noContent==0, that means that the content is needed and the disk read should occur at that point.
      Parameters:
      pageNumber - Page number to fetch
      read - Do not bother reading content from disk if false
      Returns:
      Throws:
      SqlJetException
    • getPage

      ISqlJetPage getPage(int pageNumber) throws SqlJetException
      Just call acquire( pageNumber, true);
      Parameters:
      pageNumber - Page number to fetch
      Returns:
      Throws:
      SqlJetException
    • lookupPage

      ISqlJetPage lookupPage(int pageNumber) throws SqlJetException
      Acquire a page if it is already in the in-memory cache. Do not read the page from disk. Return a pointer to the page, or null if the page is not in cache. See also getPage(int). The difference between this routine and getPage(int) is that getPage(int) will go to the disk and read in the page if the page is not already in cache. This routine returns null if the page is not in cache or if a disk I/O error has ever happened.
      Parameters:
      pageNumber - Page number to lookup
      Returns:
      Throws:
      SqlJetException
    • begin

      void begin(boolean exclusive) throws SqlJetException
      Acquire a write-lock on the database. The lock is removed when the any of the following happen:
      • commitPhaseTwo() is called.
      • rollback() is called.
      • close() is called.
      • unref() is called to on every outstanding page.
      The parameter indicates how much space in bytes to reserve for a master journal file-name at the start of the journal when it is created. A journal file is opened if this is not a temporary file. For temporary files, the opening of the journal file is deferred until there is an actual need to write to the journal. If the database is already reserved for writing, this routine is a no-op. If exclusive is true, go ahead and get an EXCLUSIVE lock on the file immediately instead of waiting until we try to flush the cache. The exclusive is ignored if a transaction is already active.
      Parameters:
      exclusive -
      Throws:
      SqlJetException
    • commitPhaseOne

      void commitPhaseOne(String master, boolean noSync) throws SqlJetException
      Sync the database file for the pager pPager. zMaster points to the name of a master journal file that should be written into the individual journal file. zMaster may be NULL, which is interpreted as no master journal (a single database transaction). This routine ensures that the journal is synced, all dirty pages written to the database file and the database file synced. The only thing that remains to commit the transaction is to delete the journal file (or master journal file if specified). Note that if zMaster==NULL, this does not overwrite a previous value passed to an sqlite3PagerCommitPhaseOne() call. If the final parameter - noSync - is true, then the database file itself is not synced. The caller must call sqlite3PagerSync() directly to sync the database file before calling CommitPhaseTwo() to delete the journal file in this case.
      Parameters:
      master -
      noSync -
      Throws:
      SqlJetException
    • commitPhaseTwo

      void commitPhaseTwo() throws SqlJetException
      Commit all changes to the database and release the write lock. If the commit fails for any reason, a rollback attempt is made and an error code is returned. If the commit worked, SQLITE_OK is returned.
      Throws:
      SqlJetException
    • rollback

      void rollback() throws SqlJetException
      Rollback all changes. The database falls back to PAGER_SHARED mode. All in-memory cache pages revert to their original data contents. The journal is deleted. This routine cannot fail unless some other process is not following the correct locking protocol or unless some other process is writing trash into the journal file (SQLITE_CORRUPT) or unless a prior malloc() failed (SQLITE_NOMEM). Appropriate error codes are returned for all these occasions. Otherwise, SQLITE_OK is returned.
      Throws:
      SqlJetException
    • getRefCount

      int getRefCount()
      Return the number of references to the pager.
      Returns:
    • sync

      void sync() throws SqlJetIOException
      Sync the pager file to disk.
      Throws:
      SqlJetIOException
    • openSavepoint

      void openSavepoint(int nSavepoint) throws SqlJetException
      Ensure that there are at least nSavepoint savepoints open.
      Throws:
      SqlJetException
    • savepoint

      void savepoint(SqlJetSavepointOperation op, int iSavepoint) throws SqlJetException
      Parameter op is always either SAVEPOINT_ROLLBACK or SAVEPOINT_RELEASE. If it is SAVEPOINT_RELEASE, then release and destroy the savepoint with index iSavepoint. If it is SAVEPOINT_ROLLBACK, then rollback all changes that have occured since savepoint iSavepoint was created. In either case, all savepoints with an index greater than iSavepoint are destroyed. If there are less than (iSavepoint+1) active savepoints when this function is called it is a no-op.
      Throws:
      SqlJetException
    • truncateImage

      void truncateImage(int pagesNumber)
      Truncate the in-memory database file image to nPage pages. This function does not actually modify the database file on disk. It just sets the internal state of the pager object so that the truncation will be done when the current transaction is committed.
      Parameters:
      pageNumber -
    • imageSize

      int imageSize()
      Return the current size of the database file image in pages. This function differs from sqlite3PagerPagecount() in two ways: a) It may only be called when at least one reference to a database page is held. This guarantees that the database size is already known and a call to sqlite3OsFileSize() is not required. b) The return value is not adjusted for the locking page.
    • getCacheSize

      int getCacheSize()
      Returns: