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LSM API Reference


This page contains the LSM API Reference Manual. It is intended to complement the LSM User Manual.

LSM API Topics

  1. Database Runtime Environment
  2. LSM Error Codes
  3. Creating and Destroying Database Connection Handles
  4. Connecting to a Database
  5. Obtaining pointers to database environments
  6. Configuring a database connection.
  7. Compression and/or Encryption Hooks
  8. Allocating and Freeing Memory
  9. Querying a Connection For Operational Data
  10. Opening and Closing Write Transactions
  11. Writing to a Database
  12. Explicit Database Work and Checkpointing
  13. Opening and Closing Database Cursors
  14. Positioning Database Cursors
  15. Extracting Data From Database Cursors
  16. Change these!!

All LSM API Functions

lsm_begin lsm_checkpoint lsm_close lsm_commit lsm_config lsm_config_log lsm_config_work_hook lsm_csr_close lsm_csr_cmp lsm_csr_first lsm_csr_key lsm_csr_last lsm_csr_next lsm_csr_open lsm_csr_prev lsm_csr_seek lsm_csr_valid lsm_csr_value lsm_delete lsm_delete_range lsm_flush lsm_free lsm_info lsm_insert lsm_new lsm_open lsm_rollback lsm_work

All LSM API Types

lsm_compress lsm_compress lsm_env

All LSM API Constants

LSM_BUSY LSM_CANTOPEN LSM_CONFIG_AUTOCHECKPOINT LSM_CONFIG_AUTOFLUSH LSM_CONFIG_AUTOMERGE LSM_CONFIG_AUTOWORK LSM_CONFIG_BLOCK_SIZE LSM_CONFIG_GET_COMPRESSION LSM_CONFIG_MAX_FREELIST LSM_CONFIG_MMAP LSM_CONFIG_MULTIPLE_PROCESSES LSM_CONFIG_PAGE_SIZE LSM_CONFIG_SAFETY LSM_CONFIG_SET_COMPRESSION LSM_CONFIG_SET_COMPRESSION_FACTORY LSM_CONFIG_USE_LOG LSM_CORRUPT LSM_ERROR LSM_FULL LSM_INFO_ARRAY_PAGES LSM_INFO_ARRAY_STRUCTURE LSM_INFO_CHECKPOINT_SIZE LSM_INFO_DB_STRUCTURE LSM_INFO_FREELIST LSM_INFO_FREELIST_SIZE LSM_INFO_LOG_STRUCTURE LSM_INFO_NREAD LSM_INFO_NWRITE LSM_INFO_PAGE_ASCII_DUMP LSM_INFO_PAGE_HEX_DUMP LSM_INFO_TREE_SIZE LSM_IOERR LSM_MISUSE LSM_MUTEX_GLOBAL LSM_MUTEX_HEAP LSM_NOMEM LSM_OK LSM_PROTOCOL LSM_SAFETY_FULL LSM_SAFETY_NORMAL LSM_SAFETY_OFF LSM_SEEK_EQ LSM_SEEK_GE LSM_SEEK_LE LSM_SEEK_LEFAST

Database Runtime Environment

struct lsm_env {
  int nByte;                 /* Size of this structure in bytes */
  int iVersion;              /* Version number of this structure (1) */
  /****** file i/o ***********************************************/
  void *pVfsCtx;
  int (*xFullpath)(lsm_env*, const char *, char *, int *);
  int (*xOpen)(lsm_env*, const char *, lsm_file **);
  int (*xRead)(lsm_file *, lsm_i64, void *, int);
  int (*xWrite)(lsm_file *, lsm_i64, void *, int);
  int (*xTruncate)(lsm_file *, lsm_i64);
  int (*xSync)(lsm_file *);
  int (*xSectorSize)(lsm_file *);
  int (*xRemap)(lsm_file *, lsm_i64, void **, lsm_i64*);
  int (*xFileid)(lsm_file *, void *pBuf, int *pnBuf);
  int (*xClose)(lsm_file *);
  int (*xUnlink)(lsm_env*, const char *);
  int (*xLock)(lsm_file*, int, int);
  int (*xShmMap)(lsm_file*, int, int, void **);
  void (*xShmBarrier)(void);
  int (*xShmUnmap)(lsm_file*, int);
  /****** memory allocation ****************************************/
  void *pMemCtx;
  void *(*xMalloc)(lsm_env*, int);            /* malloc(3) function */
  void *(*xRealloc)(lsm_env*, void *, int);   /* realloc(3) function */
  void (*xFree)(lsm_env*, void *);            /* free(3) function */
  sqlite4_size_t (*xSize)(lsm_env*, void *);  /* xSize function */
  /****** mutexes ****************************************************/
  void *pMutexCtx;
  int (*xMutexStatic)(lsm_env*,int,lsm_mutex**); /* Obtain a static mutex */
  int (*xMutexNew)(lsm_env*, lsm_mutex**);       /* Get a new dynamic mutex */
  void (*xMutexDel)(lsm_mutex *);           /* Delete an allocated mutex */
  void (*xMutexEnter)(lsm_mutex *);         /* Grab a mutex */
  int (*xMutexTry)(lsm_mutex *);            /* Attempt to obtain a mutex */
  void (*xMutexLeave)(lsm_mutex *);         /* Leave a mutex */
  int (*xMutexHeld)(lsm_mutex *);           /* Return true if mutex is held */
  int (*xMutexNotHeld)(lsm_mutex *);        /* Return true if mutex not held */
  /****** other ****************************************************/
  int (*xSleep)(lsm_env*, int microseconds);
  /* New fields may be added in future releases, in which case the
  ** iVersion value will increase. */
};
#define LSM_MUTEX_GLOBAL 1
#define LSM_MUTEX_HEAP   2

Run-time environment used by LSM Values that may be passed as the second argument to xMutexStatic.

LSM Error Codes

#define LSM_OK         0
#define LSM_ERROR      1
#define LSM_BUSY       5
#define LSM_NOMEM      7
#define LSM_IOERR     10
#define LSM_CORRUPT   11
#define LSM_FULL      13
#define LSM_CANTOPEN  14
#define LSM_PROTOCOL  15
#define LSM_MISUSE    21

Creating and Destroying Database Connection Handles

int lsm_new(lsm_env*, lsm_db **ppDb);
int lsm_close(lsm_db *pDb);

Open and close a database connection handle.

Connecting to a Database

int lsm_open(lsm_db *pDb, const char *zFilename);

Obtaining pointers to database environments

lsm_env *lsm_get_env(lsm_db *pDb);
lsm_env *lsm_default_env(void);

Return a pointer to the environment used by the database connection passed as the first argument. Assuming the argument is valid, this function always returns a valid environment pointer - it cannot fail. The lsm_default_env() function returns a pointer to the default LSM environment for the current platform.

Configuring a database connection.

int lsm_config(lsm_db *, int, ...);
#define LSM_CONFIG_AUTOFLUSH                1
#define LSM_CONFIG_PAGE_SIZE                2
#define LSM_CONFIG_SAFETY                   3
#define LSM_CONFIG_BLOCK_SIZE               4
#define LSM_CONFIG_AUTOWORK                 5
#define LSM_CONFIG_MMAP                     7
#define LSM_CONFIG_USE_LOG                  8
#define LSM_CONFIG_AUTOMERGE                9
#define LSM_CONFIG_MAX_FREELIST            10
#define LSM_CONFIG_MULTIPLE_PROCESSES      11
#define LSM_CONFIG_AUTOCHECKPOINT          12
#define LSM_CONFIG_SET_COMPRESSION         13
#define LSM_CONFIG_GET_COMPRESSION         14
#define LSM_CONFIG_SET_COMPRESSION_FACTORY 15
#define LSM_SAFETY_OFF    0
#define LSM_SAFETY_NORMAL 1
#define LSM_SAFETY_FULL   2

The lsm_config() function is used to configure a database connection. The following values may be passed as the second argument to lsm_config().

LSM_CONFIG_AUTOFLUSH
A read/write integer parameter.

This value determines the amount of data allowed to accumulate in a live in-memory tree before it is marked as old. After committing a transaction, a connection checks if the size of the live in-memory tree, including data structure overhead, is greater than the value of this option in KB. If it is, and there is not already an old in-memory tree, the live in-memory tree is marked as old.

The maximum allowable value is 1048576 (1GB). There is no minimum value. If this parameter is set to zero, then an attempt is made to mark the live in-memory tree as old after each transaction is committed.

The default value is 1024 (1MB).

LSM_CONFIG_PAGE_SIZE
A read/write integer parameter. This parameter may only be set before lsm_open() has been called.

LSM_CONFIG_BLOCK_SIZE
A read/write integer parameter.

This parameter may only be set before lsm_open() has been called. It must be set to a power of two between 64 and 65536, inclusive (block sizes between 64KB and 64MB).

If the connection creates a new database, the block size of the new database is set to the value of this option in KB. After lsm_open() has been called, querying this parameter returns the actual block size of the opened database.

The default value is 1024 (1MB blocks).

LSM_CONFIG_SAFETY
A read/write integer parameter. Valid values are 0, 1 (the default) and 2. This parameter determines how robust the database is in the face of a system crash (e.g. a power failure or operating system crash). As follows:

0 (off): No robustness. A system crash may corrupt the database.

1 (normal): Some robustness. A system crash may not corrupt the database file, but recently committed transactions may be lost following recovery.

2 (full): Full robustness. A system crash may not corrupt the database file. Following recovery the database file contains all successfully committed transactions.

LSM_CONFIG_AUTOWORK
A read/write integer parameter.

LSM_CONFIG_AUTOCHECKPOINT
A read/write integer parameter.

If this option is set to non-zero value N, then a checkpoint is automatically attempted after each N KB of data have been written to the database file.

The amount of uncheckpointed data already written to the database file is a global parameter. After performing database work (writing to the database file), the process checks if the total amount of uncheckpointed data exceeds the value of this paramter. If so, a checkpoint is performed. This means that this option may cause the connection to perform a checkpoint even if the current connection has itself written very little data into the database file.

The default value is 2048 (checkpoint every 2MB).

LSM_CONFIG_MMAP
A read/write integer parameter. True to use mmap() to access the database file. False otherwise.

LSM_CONFIG_USE_LOG
A read/write boolean parameter. True (the default) to use the log file normally. False otherwise.

LSM_CONFIG_AUTOMERGE
A read/write integer parameter. The minimum number of segments to merge together at a time. Default value 4.

LSM_CONFIG_MAX_FREELIST
A read/write integer parameter. The maximum number of free-list entries that are stored in a database checkpoint (the others are stored elsewhere in the database).

There is no reason for an application to configure or query this parameter. It is only present because configuring a small value makes certain parts of the lsm code easier to test.

LSM_CONFIG_MULTIPLE_PROCESSES
A read/write boolean parameter. This parameter may only be set before lsm_open() has been called. If true, the library uses shared-memory and posix advisory locks to co-ordinate access by clients from within multiple processes. Otherwise, if false, all database clients must be located in the same process. The default value is true.

LSM_CONFIG_SET_COMPRESSION
Set the compression methods used to compress and decompress database content. The argument to this option should be a pointer to a structure of type lsm_compress. The lsm_config() method takes a copy of the structures contents.

This option may only be used before lsm_open() is called. Invoking it after lsm_open() has been called results in an LSM_MISUSE error.

LSM_CONFIG_GET_COMPRESSION
Query the compression methods used to compress and decompress database content.

LSM_CONFIG_SET_COMPRESSION_FACTORY
Configure a factory method to be invoked in case of an LSM_MISMATCH error.

Compression and/or Encryption Hooks

struct lsm_compress {
  void *pCtx;
  unsigned int iId;
  int (*xBound)(void *, int nSrc);
  int (*xCompress)(void *, char *, int *, const char *, int);
  int (*xUncompress)(void *, char *, int *, const char *, int);
  void (*xFree)(void *pCtx);
};
struct lsm_compress_factory {
  void *pCtx;
  int (*xFactory)(void *, lsm_db *, u32);
  void (*xFree)(void *pCtx);
};

Allocating and Freeing Memory

void *lsm_malloc(lsm_env*, size_t);
void *lsm_realloc(lsm_env*, void *, size_t);
void lsm_free(lsm_env*, void *);

Invoke the memory allocation functions that belong to environment pEnv. Or the system defaults if no memory allocation functions have been registered.

Querying a Connection For Operational Data

int lsm_info(lsm_db *, int, ...);
#define LSM_INFO_NWRITE           1
#define LSM_INFO_NREAD            2
#define LSM_INFO_DB_STRUCTURE     3
#define LSM_INFO_LOG_STRUCTURE    4
#define LSM_INFO_ARRAY_STRUCTURE  5
#define LSM_INFO_PAGE_ASCII_DUMP  6
#define LSM_INFO_PAGE_HEX_DUMP    7
#define LSM_INFO_FREELIST         8
#define LSM_INFO_ARRAY_PAGES      9
#define LSM_INFO_CHECKPOINT_SIZE 10
#define LSM_INFO_TREE_SIZE       11
#define LSM_INFO_FREELIST_SIZE   12

Query a database connection for operational statistics or data. The following values may be passed as the second argument to lsm_info().

LSM_INFO_NWRITE
The third parameter should be of type (int *). The location pointed to by the third parameter is set to the number of 4KB pages written to the database file during the lifetime of this connection.

LSM_INFO_NREAD
The third parameter should be of type (int *). The location pointed to by the third parameter is set to the number of 4KB pages read from the database file during the lifetime of this connection.

LSM_INFO_DB_STRUCTURE
The third argument should be of type (char **). The location pointed to is populated with a pointer to a nul-terminated string containing the string representation of a Tcl data-structure reflecting the current structure of the database file. Specifically, the current state of the worker snapshot. The returned string should be eventually freed by the caller using lsm_free().

The returned list contains one element for each level in the database, in order from most to least recent. Each element contains a single element for each segment comprising the corresponding level, starting with the lhs segment, then each of the rhs segments (if any) in order from most to least recent.

Each segment element is itself a list of 4 integer values, as follows:

  1. First page of segment
  2. Last page of segment
  3. Root page of segment (if applicable)
  4. Total number of pages in segment

LSM_INFO_ARRAY_STRUCTURE
There should be two arguments passed following this option (i.e. a total of four arguments passed to lsm_info()). The first argument should be the page number of the first page in a database array (perhaps obtained from an earlier INFO_DB_STRUCTURE call). The second trailing argument should be of type (char **). The location pointed to is populated with a pointer to a nul-terminated string that must be eventually freed using lsm_free() by the caller.

The output string contains the text representation of a Tcl list of integers. Each pair of integers represent a range of pages used by the identified array. For example, if the array occupies database pages 993 to 1024, then pages 2048 to 2777, then the returned string will be "993 1024 2048 2777".

If the specified integer argument does not correspond to the first page of any database array, LSM_ERROR is returned and the output pointer is set to a NULL value.

LSM_INFO_LOG_STRUCTURE
The third argument should be of type (char **). The location pointed to is populated with a pointer to a nul-terminated string containing the string representation of a Tcl data-structure. The returned string should be eventually freed by the caller using lsm_free().

The Tcl structure returned is a list of six integers that describe the current structure of the log file.

LSM_INFO_ARRAY_PAGES

LSM_INFO_PAGE_ASCII_DUMP
As with LSM_INFO_ARRAY_STRUCTURE, there should be two arguments passed with calls that specify this option - an integer page number and a (char **) used to return a nul-terminated string that must be later freed using lsm_free(). In this case the output string is populated with a human-readable description of the page content.

If the page cannot be decoded, it is not an error. In this case the human-readable output message will report the systems failure to interpret the page data.

LSM_INFO_PAGE_HEX_DUMP
This argument is similar to PAGE_ASCII_DUMP, except that keys and values are represented using hexadecimal notation instead of ascii.

LSM_INFO_FREELIST
The third argument should be of type (char **). The location pointed to is populated with a pointer to a nul-terminated string containing the string representation of a Tcl data-structure. The returned string should be eventually freed by the caller using lsm_free().

The Tcl structure returned is a list containing one element for each free block in the database. The element itself consists of two integers - the block number and the id of the snapshot that freed it.

LSM_INFO_CHECKPOINT_SIZE
The third argument should be of type (int *). The location pointed to by this argument is populated with the number of KB written to the database file since the most recent checkpoint.

LSM_INFO_TREE_SIZE
If this value is passed as the second argument to an lsm_info() call, it should be followed by two arguments of type (int *) (for a total of four arguments).

At any time, there are either one or two tree structures held in shared memory that new database clients will access (there may also be additional tree structures being used by older clients - this API does not provide information on them). One tree structure - the current tree - is used to accumulate new data written to the database. The other tree structure - the old tree - is a read-only tree holding older data and may be flushed to disk at any time.

Assuming no error occurs, the location pointed to by the first of the two (int *) arguments is set to the size of the old in-memory tree in KB. The second is set to the size of the current, or live in-memory tree.

Opening and Closing Write Transactions

int lsm_begin(lsm_db *pDb, int iLevel);
int lsm_commit(lsm_db *pDb, int iLevel);
int lsm_rollback(lsm_db *pDb, int iLevel);

These functions are used to open and close transactions and nested sub-transactions.

The lsm_begin() function is used to open transactions and sub-transactions. A successful call to lsm_begin() ensures that there are at least iLevel nested transactions open. To open a top-level transaction, pass iLevel=1. To open a sub-transaction within the top-level transaction, iLevel=2. Passing iLevel=0 is a no-op.

lsm_commit() is used to commit transactions and sub-transactions. A successful call to lsm_commit() ensures that there are at most iLevel nested transactions open. To commit a top-level transaction, pass iLevel=0. To commit all sub-transactions inside the main transaction, pass iLevel=1.

Function lsm_rollback() is used to roll back transactions and sub-transactions. A successful call to lsm_rollback() restores the database to the state it was in when the iLevel'th nested sub-transaction (if any) was first opened. And then closes transactions to ensure that there are at most iLevel nested transactions open. Passing iLevel=0 rolls back and closes the top-level transaction. iLevel=1 also rolls back the top-level transaction, but leaves it open. iLevel=2 rolls back the sub-transaction nested directly inside the top-level transaction (and leaves it open).

Writing to a Database

int lsm_insert(lsm_db*, const void *pKey, int nKey, const void *pVal, int nVal);
int lsm_delete(lsm_db *, const void *pKey, int nKey);
int lsm_delete_range(lsm_db *, 
    const void *pKey1, int nKey1, const void *pKey2, int nKey2
);

Write a new value into the database. If a value with a duplicate key already exists it is replaced. Delete a value from the database. No error is returned if the specified key value does not exist in the database. Delete all database entries with keys that are greater than (pKey1/nKey1) and smaller than (pKey2/nKey2). Note that keys (pKey1/nKey1) and (pKey2/nKey2) themselves, if they exist in the database, are not deleted.

Return LSM_OK if successful, or an LSM error code otherwise.

Explicit Database Work and Checkpointing

int lsm_work(lsm_db *pDb, int nMerge, int nKB, int *pnWrite);
int lsm_flush(lsm_db *pDb);
int lsm_checkpoint(lsm_db *pDb, int *pnKB);

This function is called by a thread to work on the database structure. Attempt to checkpoint the current database snapshot. Return an LSM error code if an error occurs or LSM_OK otherwise.

If the current snapshot has already been checkpointed, calling this function is a no-op. In this case if pnKB is not NULL, *pnKB is set to 0. Or, if the current snapshot is successfully checkpointed by this function and pbKB is not NULL, *pnKB is set to the number of bytes written to the database file since the previous checkpoint (the same measure as returned by the LSM_INFO_CHECKPOINT_SIZE query).

Opening and Closing Database Cursors

int lsm_csr_open(lsm_db *pDb, lsm_cursor **ppCsr);
int lsm_csr_close(lsm_cursor *pCsr);

Open and close a database cursor.

Positioning Database Cursors

int lsm_csr_seek(lsm_cursor *pCsr, const void *pKey, int nKey, int eSeek);
int lsm_csr_first(lsm_cursor *pCsr);
int lsm_csr_last(lsm_cursor *pCsr);
int lsm_csr_next(lsm_cursor *pCsr);
int lsm_csr_prev(lsm_cursor *pCsr);
#define LSM_SEEK_LEFAST   -2
#define LSM_SEEK_LE       -1
#define LSM_SEEK_EQ        0
#define LSM_SEEK_GE        1

If the fourth parameter is LSM_SEEK_EQ, LSM_SEEK_GE or LSM_SEEK_LE, this function searches the database for an entry with key (pKey/nKey). If an error occurs, an LSM error code is returned. Otherwise, LSM_OK.

If no error occurs and the requested key is present in the database, the cursor is left pointing to the entry with the specified key. Or, if the specified key is not present in the database the state of the cursor depends on the value passed as the final parameter, as follows:

LSM_SEEK_EQ
The cursor is left at EOF (invalidated). A call to lsm_csr_valid() returns non-zero.

LSM_SEEK_LE
The cursor is left pointing to the largest key in the database that is smaller than (pKey/nKey). If the database contains no keys smaller than (pKey/nKey), the cursor is left at EOF.

LSM_SEEK_GE
The cursor is left pointing to the smallest key in the database that is larger than (pKey/nKey). If the database contains no keys larger than (pKey/nKey), the cursor is left at EOF.

If the fourth parameter is LSM_SEEK_LEFAST, this function searches the database in a similar manner to LSM_SEEK_LE, with two differences:

  1. Even if a key can be found (the cursor is not left at EOF), the lsm_csr_value() function may not be used (attempts to do so return LSM_MISUSE).

  2. The key that the cursor is left pointing to may be one that has been recently deleted from the database. In this case it is guaranteed that the returned key is larger than any key currently in the database that is less than or equal to (pKey/nKey).

LSM_SEEK_LEFAST requests are intended to be used to allocate database keys. Advance the specified cursor to the next or previous key in the database. Return LSM_OK if successful, or an LSM error code otherwise.

Functions lsm_csr_seek(), lsm_csr_first() and lsm_csr_last() are "seek" functions. Whether or not lsm_csr_next and lsm_csr_prev may be called successfully also depends on the most recent seek function called on the cursor. Specifically:

Otherwise, if the above conditions are not met when lsm_csr_next or lsm_csr_prev is called, LSM_MISUSE is returned and the cursor position remains unchanged. Values that may be passed as the fourth argument to lsm_csr_seek().

Extracting Data From Database Cursors

int lsm_csr_valid(lsm_cursor *pCsr);
int lsm_csr_key(lsm_cursor *pCsr, const void **ppKey, int *pnKey);
int lsm_csr_value(lsm_cursor *pCsr, const void **ppVal, int *pnVal);
int lsm_csr_cmp(lsm_cursor *pCsr, const void *pKey, int nKey, int *piRes);

Retrieve data from a database cursor. If no error occurs, this function compares the database key passed via the pKey/nKey arguments with the key that the cursor passed as the first argument currently points to. If the cursors key is less than, equal to or greater than pKey/nKey, *piRes is set to less than, equal to or greater than zero before returning. LSM_OK is returned in this case.

Or, if an error occurs, an LSM error code is returned and the final value of *piRes is undefined. If the cursor does not point to a valid key when this function is called, LSM_MISUSE is returned.

Change these!!

void lsm_config_log(lsm_db *, void (*)(void *, int, const char *), void *);
void lsm_config_work_hook(lsm_db *, void (*)(lsm_db *, void *), void *);

Configure a callback to which debugging and other messages should be directed. Only useful for debugging lsm. Configure a callback that is invoked if the database connection ever writes to the database file.