NNAAMMEE Db - database access class SSYYNNOOPPSSIISS ##iinncclluuddee <> ssttaattiicc iinntt DDbb::::ooppeenn((ccoonnsstt cchhaarr **ffnnaammee,, DDBBTTYYPPEE ttyyppee,, uu__iinntt3322__tt ffllaaggss,, iinntt mmooddee,, DDbbEEnnvv **ddbbeennvv,, DDbbIInnffoo **ddbbiinnffoo,, DDbb ****ddbbpppp));; DDBBTTYYPPEE DDbb::::ggeett__ttyyppee((vvooiidd)) ccoonnsstt;; iinntt DDbb::::cclloossee((uu__iinntt3322__tt ffllaaggss));; iinntt DDbb::::ccuurrssoorr((DDbbTTxxnn **ttxxnniidd,, DDbbcc ****ccuurrssoorrpp));; iinntt DDbb::::ddeell((DDbbtt **kkeeyy,, DDbbTTxxnn **ttxxnniidd));; iinntt DDbb::::ffdd((iinntt **ffddpp));; iinntt DDbb::::ggeett((DDbbTTxxnn **ttxxnniidd,, DDbbtt **kkeeyy,, DDbbtt **ddaattaa,, uu__iinntt3322__tt ffllaaggss));; iinntt DDbb::::ppuutt((DDbbTTxxnn **ttxxnniidd,, DDbbtt **kkeeyy,, DDbbtt **ddaattaa,, uu__iinntt3322__tt ffllaaggss));; iinntt DDbb::::ssttaatt((vvooiidd **sspp,, vvooiidd **((**ddbb__mmaalllloocc))((ssiizzee__tt)),, uu__iinntt3322__tt ffllaaggss));; iinntt DDbb::::ssyynncc((uu__iinntt3322__tt ffllaaggss));; DDEESSCCRRIIPPTTIIOONN The DB library is a family of classes that provides a mod- ular programming interface to transactions and record-ori- ented file access. The library includes support for transactions, locking, logging and file page caching, as well as various indexed access methods. Many of the classes (e.g., the file page caching class) are useful independent of the other DB classes, although some classes are explicitly based on other classes (e.g., transactions and logging). For a general description of the DB pack- age, see _d_b___i_n_t_r_o(3). This manual page describes the Db class, which is the cen- ter of access activity. The currently supported file formats are btree, hashed and recno. The btree format is a representation of a sorted, balanced tree structure. The hashed format is an extensi- ble, dynamic hashing scheme. The recno format supports fixed or variable length records (optionally retrieved from a flat text file). Storage and retrieval for the Db access methods are based on key/data pairs, using the Dbt class. See _D_b_t(3) for specific information on the structure and capabilities of a Dbt. The _D_b_:_:_o_p_e_n method opens the database represented by _f_i_l_e for both reading and writing. Files never intended to be shared or preserved on disk may be created by setting the file parameter to NULL. The _D_b_:_:_o_p_e_n method copies a pointer to a Db object into the memory location referenced by _d_b_p_p. The methods of this object allow you to perform various database actions, as described below. The _D_b_:_:_o_p_e_n method throws a _D_b_E_x_c_e_p_- _t_i_o_n(3) or returns the value of _e_r_r_n_o on failure and 0 on success. Note, while most of the access methods use _f_i_l_e as the name of an underlying file on disk, this is not guaran- teed. Also, calling _D_b_:_:_o_p_e_n is a reasonably expensive operation. (This is based on a model where the DBMS keeps a set of files open for a long time rather than opening and closing them on each query.) The _t_y_p_e argument is of type DBTYPE (as defined in the include file) and must be set to one of DB_BTREE, DB_HASH, DB_RECNO or DB_UNKNOWN. If _t_y_p_e is DB_UNKNOWN, the database must already exist and _D_b_:_:_o_p_e_n will then determine if it is of type DB_BTREE, DB_HASH or DB_RECNO. The _f_l_a_g_s and _m_o_d_e arguments specify how files will be opened and/or created when they don't already exist. The flags value is specified by oorr'ing together one or more of the following values: DB_CREATE Create any underlying files, as necessary. If the files do not already exist and the DB_CREATE flag is not specified, the call will fail. DB_NOMMAP Do not map this file (see _D_b_M_p_o_o_l(3) for further information). DB_RDONLY Open the database for reading only. Any attempt to write the database using the access methods will fail regardless of the actual permissions of any underly- ing files. DB_THREAD Cause the Db handle returned by the _D_b_:_:_o_p_e_n method to be useable by multiple threads within a single address space, i.e., to be ``free-threaded''. DB_TRUNCATE ``Truncate'' the database if it exists, i.e., behave as if the database were just created, discarding any previous contents. All files created by the access methods are created with mode _m_o_d_e (as described in _c_h_m_o_d(2)) and modified by the process' umask value at the time of creation (see _u_m_a_s_k(2)). The group ownership of created files is based on the system and directory defaults, and is not further specified by DB. See _D_b_E_n_v(3) for a description of the _d_b_e_n_v argument, and _D_b_I_n_f_o(3) for a description of the _d_b_i_n_f_o argument. DDbb OOPPEERRAATTIIOONNSS The Db object returned by _D_b_:_:_o_p_e_n describes a database type, and includes a set of functions to perform various actions, as described below. The methods for Db are as follows: DBTYPE Db::get_type(void); The type of the underlying access method (and file format). Returns one of DB_BTREE, DB_HASH or DB_RECNO. This value may be used to determine the type of the database after a return from _D_b_:_:_o_p_e_n with the _t_y_p_e argument set to DB_UNKNOWN. int Db::close(u_int32_t flags); A method to flush any cached information to disk, close any open cursors (see _D_b_c(3)), free any allo- cated resources, and close any underlying files. Since key/data pairs are cached in memory, failing to sync the file with the _c_l_o_s_e or _s_y_n_c method may result in inconsistent or lost information. The _f_l_a_g_s parameter must be set to 0 or the following value: DB_NOSYNC Do not flush cached information to disk. The DB_NOSYNC flag is a dangerous option. It should only be set if the application is doing logging (with transactions) so that the database is recoverable after a system or application crash, or if the database is always generated from scratch after any system or application crash. IItt iiss iimmppoorrttaanntt ttoo uunnddeerrssttaanndd tthhaatt fflluusshhiinngg ccaacchheedd iinnffoorrmmaattiioonn ttoo ddiisskk oonnllyy mmiinniimmiizzeess tthhee wwiinnddooww ooff ooppppoorrttuunniittyy ffoorr ccoorrrruupptteedd ddaattaa.. While unlikely, it is possible for database corruption to happen if a system or application crash occurs while writing data to the database. To ensure that database corruption never occurs, applications must either: use transac- tions and logging with automatic recovery, use log- ging and application-specific recovery, or edit a copy of the database, and, once all applications using the database have successfully called _c_l_o_s_e, replace the original database with the updated copy. When multiple threads are using the Db handle concur- rently, only a single thread may call the Db handle close method. The _c_l_o_s_e method throws a _D_b_E_x_c_e_p_t_i_o_n(3) or returns the value of _e_r_r_n_o on failure and 0 on success. int Db::cursor(DbTxn *txnid, Dbc **cursorp); A method to create a cursor and copy a pointer to it into the memory referenced by _c_u_r_s_o_r_p. A cursor is an object used to provide sequential access through a database. If the file is being accessed under transaction pro- tection, the _t_x_n_i_d parameter is a transaction ID returned from _t_x_n___b_e_g_i_n, otherwise, NULL. If trans- action protection is enabled, cursors must be opened and closed within the context of a transaction, and the _t_x_n_i_d parameter specifies the transaction context in which the cursor may be used. See _D_b_c(3) for more information. The _c_u_r_s_o_r method throws a _D_b_E_x_c_e_p_t_i_o_n(3) or returns the value of _e_r_r_n_o on failure and 0 on success. int Db::del(DbTxn *txnid, Dbt *key, u_int32_t flags); A method to remove key/data pairs from the database. The key/data pair associated with the specified _k_e_y is discarded from the database. In the presence of duplicate key values, all records associated with the designated key will be discarded. If the file is being accessed under transaction protection, the _t_x_n_i_d parameter is a transaction ID returned from _t_x_n___b_e_g_i_n, otherwise, NULL. The _f_l_a_g_s parameter is currently unused, and must be set to 0. The _d_e_l method throws a _D_b_E_x_c_e_p_t_i_o_n(3) or returns the value of _e_r_r_n_o on failure, 0 on success, and DB_NOT- FOUND if the specified _k_e_y did not exist in the file. int Db::fd(int *fdp); A method that copies a file descriptor representative of the underlying database into the memory referenced by _f_d_p. A file descriptor referencing the same file will be returned to all processes that call _D_b_:_:_o_p_e_n with the same _f_i_l_e argument. This file descriptor may be safely used as an argument to the _f_c_n_t_l(2) and _f_l_o_c_k(2) locking functions. The file descriptor is not necessarily associated with any of the underlying files used by the access method. The _f_d method only supports a coarse-grained form of locking. Applications should use the lock manager where possible. The _f_d method throws a _D_b_E_x_c_e_p_t_i_o_n(3) or returns the value of _e_r_r_n_o on failure and 0 on success. int Db::get(DbTxn *txnid, Dbt *key, Dbt *data, u_int32_t flags); A method that is an interface for keyed retrieval from the database. The address and length of the data associated with the specified _k_e_y are returned in the object referenced by _d_a_t_a. In the presence of duplicate key values, _g_e_t will return the first data item for the designated key. Duplicates are sorted by insert order except where this order has been overridden by cursor operations. RReettrriieevvaall ooff dduupplliiccaatteess rreeqquuiirreess tthhee uussee ooff ccuurrssoorr ooppeerraattiioonnss.. See _D_b_c(3) for details. If the file is being accessed under transaction pro- tection, the _t_x_n_i_d parameter is a transaction ID returned from _t_x_n___b_e_g_i_n, otherwise, NULL. The _f_l_a_g_s parameter must be set to 0 or the following value: DB_GET_RECNO Retrieve a specific numbered record from a database. Upon return, both the _k_e_y and _d_a_t_a items will have been filled in, not just the data item as is done for all other uses of the _g_e_t method. For DB_GET_RECNO to be specified, the underlying database must be of type btree, and it must have been created with the DB_RECNUM flag (see _D_b_:_:_o_p_e_n(3)). In this case, the _d_a_t_a field of the _k_e_y must be a pointer to a memory location of type _d_b___r_e_c_n_o___t, as described in _D_b_t(3). If the database is a recno database and the requested key exists, but was never explicitly created by the application or was later deleted, the _g_e_t method returns DB_KEYEMPTY. Otherwise, if the requested key isn't in the database, the _g_e_t method returns DB_NOT- FOUND. Otherwise, the _g_e_t method throws a _D_b_E_x_c_e_p_- _t_i_o_n(3) or returns the value of _e_r_r_n_o on failure and 0 on success. int Db::put(DbTxn *txnid, Dbt *key, Dbt *data, u_int32_t flags); A method to store key/data pairs in the database. If the database supports duplicates, the _p_u_t method adds the new data value at the end of the duplicate set. If the file is being accessed under transaction pro- tection, the _t_x_n_i_d parameter is a transaction ID returned from _t_x_n___b_e_g_i_n, otherwise, NULL. The flags value is specified by oorr'ing together one or more of the following values: DB_APPEND Append the key/data pair to the end of the database. For DB_APPEND to be specified, the underlying database must be of type recno. The record number allocated to the record is returned in the specified _k_e_y. DB_NOOVERWRITE Enter the new key/data pair only if the key does not already appear in the database. The default behavior of the _p_u_t method is to enter the new key/data pair, replacing any previously existing key if duplicates are disallowed, or to add a duplicate entry if duplicates are allowed. Even if the designated database allows duplicates, a call to _p_u_t with the DB_NOOVERWRITE flag set will fail if the key already exists in the database. The _p_u_t method throws a _D_b_E_x_c_e_p_t_i_o_n(3) or returns the value of _e_r_r_n_o on failure, 0 on success, and DB_KEYEXIST if the DB_NOOVERWRITE _f_l_a_g was set and the key already exists in the file. int Db::sync(u_int32_t flags); A method to flush any cached information to disk. If the database is in memory only, the _s_y_n_c method has no effect and will always succeed. The _f_l_a_g_s parameter is currently unused, and must be set to 0. See the _c_l_o_s_e method description above for a discus- sion of Db and cached data. The _s_y_n_c method throws a _D_b_E_x_c_e_p_t_i_o_n(3) or returns the value of _e_r_r_n_o on failure and 0 on success. int Db::stat(void *sp, void *(*db_malloc)(size_t), u_int32_t flags); A method to create a statistical structure and copy a pointer to it into user-specified memory locations. Specifically, if _s_p is non-NULL, a pointer to the statistics for the database are copied into the mem- ory location it references. Statistical structures are created in allocated mem- ory. If _d_b___m_a_l_l_o_c is non-NULL, it is called to allo- cate the memory, otherwise, the library function _m_a_l_- _l_o_c(3) is used. The function _d_b___m_a_l_l_o_c must match the calling conventions of the _m_a_l_l_o_c(3) library rou- tine. Regardless, the caller is responsible for deallocating the returned memory. To deallocate the returned memory, free each returned memory pointer; pointers inside the memory do not need to be individ- ually freed. IInn tthhee pprreesseennccee ooff mmuullttiippllee tthhrreeaaddss oorr pprroocceesssseess aacccceessssiinngg aann aaccttiivvee ddaattaabbaassee,, tthhee rreettuurrnneedd iinnffoorrmmaa-- ttiioonn mmaayy bbee oouutt--ooff--ddaattee.. TThhiiss mmeetthhoodd mmaayy aacccceessss aallll ooff tthhee ppaaggeess iinn tthhee ddaattaabbaassee,, aanndd tthheerreeffoorree mmaayy iinnccuurr aa sseevveerree ppeerrffoorr-- mmaannccee ppeennaallttyy aanndd hhaavvee oobbvviioouuss nneeggaattiivvee eeffffeeccttss oonn tthhee uunnddeerrllyyiinngg bbuuffffeerr ppooooll.. The _f_l_a_g_s parameter must be set to 0 or the following value: DB_RECORDCOUNT In the case of a btree or recno database, fill in the _b_t___n_r_e_c_s field, but do not collect any other information. This flag makes it reason- able for applications to request a record count from a database without incurring a performance penalty. The _s_t_a_t method throws a _D_b_E_x_c_e_p_t_i_o_n(3) or returns the value of _e_r_r_n_o on failure and 0 on success. In the case of a btree or recno database, the statis- tics are stored in a structure of type DB_BTREE_STAT (typedef'd in ). The following fields will be filled in: u_int32_t bt_magic; Magic number that identifies the file as a btree file. u_int32_t bt_version; The version of the btree file type. u_int32_t bt_flags; Permanent database flags, including DB_DUP, DB_FIXEDLEN, DB_RECNUM and DB_RENUMBER. u_int32_t bt_minkey; The _b_t___m_i_n_k_e_y value specified to _D_b_:_:_o_p_e_n(3), if any. u_int32_t bt_re_len; The _r_e___l_e_n value specified to _D_b_:_:_o_p_e_n(3), if any. u_int32_t bt_re_pad; The _r_e___p_a_d value specified to _D_b_:_:_o_p_e_n(3), if any. u_int32_t bt_pagesize; Underlying tree page size. u_int32_t bt_levels; Number of levels in the tree. u_int32_t bt_nrecs; Number of data items in the tree (since there may be multiple data items per key, this number may not be the same as the number of keys). u_int32_t bt_int_pg; Number of tree internal pages. u_int32_t bt_leaf_pg; Number of tree leaf pages. u_int32_t bt_dup_pg; Number of tree duplicate pages. u_int32_t bt_over_pg; Number of tree overflow pages. u_int32_t bt_free; Number of pages on the free list. u_int32_t bt_freed; Number of pages made available for reuse because they were emptied. u_int32_t bt_int_pgfree; Number of bytes free in tree internal pages. u_int32_t bt_leaf_pgfree; Number of bytes free in tree leaf pages. u_int32_t bt_dup_pgfree; Number of bytes free in tree duplicate pages. u_int32_t bt_over_pgfree; Number of bytes free in tree overflow pages. u_int32_t bt_pfxsaved; Number of bytes saved by prefix compression. u_int32_t bt_split; Total number of tree page splits (includes fast and root splits). u_int32_t bt_rootsplit; Number of root page splits. u_int32_t bt_fastsplit; Number of fast splits. When sorted keys are added to the database, the Db btree implementa- tion will split left or right to increase the page-fill factor. This number is a measure of how often it was possible to make such a split. u_int32_t bt_added; Number of keys added. u_int32_t bt_deleted; Number of keys deleted. u_int32_t bt_get; Number of keys retrieved. (Note, this value will not reflect any keys retrieved when the database was open for read-only access, as there is no permanent location to store the informa- tion in this case.) u_int32_t bt_cache_hit; Number of hits in tree fast-insert code. When sorted keys are added to the database, the Db btree implementation will check the last page where an insert occurred before doing a full lookup. This number is a measure of how often the lookup was successful. u_int32_t bt_cache_miss; Number of misses in tree fast-insert code. See the description of bt_cache_hit; this number is a measure of how often the lookup failed. EENNVVIIRROONNMMEENNTT VVAARRIIAABBLLEESS The following environment variables affect the execution of _D_b_:_:_o_p_e_n: DB_HOME If the _d_b_e_n_v argument to _D_b_:_:_o_p_e_n was initialized using _d_b___a_p_p_i_n_i_t, the environment variable DB_HOME may be used as the path of the database home for the interpretation of the _d_i_r argument to _D_b_:_:_o_p_e_n, as described in _d_b___a_p_p_i_n_i_t(3). Specifically, _D_b_:_:_o_p_e_n is affected by the configuration string value of DB_DATA_DIR. EEXXAAMMPPLLEESS Applications that create short-lived databases that are discarded or recreated when the system fails and are unconcerned with concurrent access and loss of data due to catastrophic failure, may wish to use the _D_b_:_:_o_p_e_n func- tionality without other parts of the Db library. Such applications will only be concerned with the Db access methods. The Db access methods will use the memory pool subsystem, but the application is unlikely to be aware of this. See the file _e_x_a_m_p_l_e_s___c_x_x_/_A_c_c_e_s_s_E_x_a_m_p_l_e_._c_p_p in the Db source distribution for a C++ language code example of how such an application might use the Db library. EERRRROORRSS Methods marked as returning _e_r_r_n_o will, by default, throw an exception that encapsulates the error information. The default error behavior can be changed, see _D_b_E_x_c_e_p_t_i_o_n(3). The _D_b_:_:_o_p_e_n method may fail and throw a _D_b_E_x_c_e_p_t_i_o_n(3) or return _e_r_r_n_o for any of the errors specified for the following DB and library functions: Db::sync(3), DbLock::get(3), DbLock::put(3), DbLockTab::id(3), DbLock- Tab::vec(3), DbLog::db_register(3), DbLog::put(3), DbM- pool::close(3), DbMpool::db_register(3), DbMpool::open(3), DbMpoolFile::close(3), DbMpoolFile::get(3), DbM- poolFile::open(3), DbMpoolFile::put(3), DbM- poolFile::set(3), DbMpoolFile::sync(3), calloc(3), close(2), fcntl(2), fflush(3), malloc(3), memcpy(3), mem- move(3), memset(3), mmap(2), munmap(2), open(2), read(2), realloc(3), sigfillset(3), sigprocmask(2), stat(2), str- cpy(3), strdup(3), strerror(3), strlen(3), time(3), and unlink(2). In addition, the _D_b_:_:_o_p_e_n method may fail and throw a _D_b_E_x_c_e_p_t_i_o_n(3) or return _e_r_r_n_o for the following condi- tions: [EAGAIN] A lock was unavailable. [EINVAL] An invalid flag value or parameter was specified (e.g., unknown database type, page size, hash method, recno pad byte, byte order) or a flag value or param- eter that is incompatible with the current _f_i_l_e spec- ification. The DB_THREAD flag was specified and spinlocks are not implemented for this architecture. There is a mismatch between the version number of _f_i_l_e and the software. A _r_e___s_o_u_r_c_e file was specified with either the DB_THREAD flag or a non-NULL _t_x___i_n_f_o field in the DbEnv argument to _D_b_:_:_o_p_e_n. [ENOENT] A non-existent _r_e___s_o_u_r_c_e file was specified. [EPERM] Database corruption was detected. All subsequent database calls (other than _D_b_:_:_c_l_o_s_e) will return EPERM. The _D_b_:_:_c_l_o_s_e method may fail and throw a _D_b_E_x_c_e_p_t_i_o_n(3) or return _e_r_r_n_o for any of the errors specified for the following DB and library functions: Db::sync(3), DbLock::get(3), DbLock::put(3), DbLockTab::vec(3), DbLog::db_register(3), DbLog::put(3), DbMpool::close(3), DbMpoolFile::close(3), DbMpoolFile::get(3), DbM- poolFile::put(3), DbMpoolFile::set(3), DbM- poolFile::sync(3), calloc(3), close(2), fflush(3), mal- loc(3), memcpy(3), memmove(3), memset(3), munmap(2), real- loc(3), and strerror(3). The _D_b_:_:_c_u_r_s_o_r method may fail and throw a _D_b_E_x_c_e_p_t_i_o_n(3) or return _e_r_r_n_o for any of the errors specified for the following DB and library functions: calloc(3). In addition, the _D_b_:_:_c_u_r_s_o_r method may fail and throw a _D_b_E_x_c_e_p_t_i_o_n(3) or return _e_r_r_n_o for the following condi- tions: [EINVAL] An invalid flag value or parameter was specified. [EPERM] Database corruption was detected. All subsequent database calls (other than _D_b_:_:_c_l_o_s_e) will return EPERM. The _D_b_:_:_d_e_l method may fail and throw a _D_b_E_x_c_e_p_t_i_o_n(3) or return _e_r_r_n_o for any of the errors specified for the following DB and library functions: DbLock::get(3), DbLock::put(3), DbLockTab::id(3), DbLockTab::vec(3), DbLog::put(3), DbMpoolFile::get(3), DbMpoolFile::put(3), DbMpoolFile::set(3), calloc(3), fcntl(2), fflush(3), mal- loc(3), memcmp(3), memcpy(3), memmove(3), memset(3), real- loc(3), and strerror(3). In addition, the _D_b_:_:_d_e_l method may fail and throw a _D_b_E_x_- _c_e_p_t_i_o_n(3) or return _e_r_r_n_o for the following conditions: [EAGAIN] A lock was unavailable. [EINVAL] An invalid flag value or parameter was specified. [EPERM] Database corruption was detected. All subsequent database calls (other than _D_b_:_:_c_l_o_s_e) will return EPERM. In addition, the _D_b_:_:_f_d method may fail and throw a _D_b_E_x_- _c_e_p_t_i_o_n(3) or return _e_r_r_n_o for the following conditions: [ENOENT] The _D_b_:_:_f_d method was called for an in-memory database, or no underlying file has yet been created. [EPERM] Database corruption was detected. All subsequent database calls (other than _D_b_:_:_c_l_o_s_e) will return EPERM. The _D_b_:_:_g_e_t method may fail and throw a _D_b_E_x_c_e_p_t_i_o_n(3) or return _e_r_r_n_o for any of the errors specified for the following DB and library functions: DbLock::get(3), DbLock::put(3), DbLockTab::id(3), DbLockTab::vec(3), DbLog::put(3), DbMpoolFile::get(3), DbMpoolFile::put(3), DbMpoolFile::set(3), Dbc::get(3), calloc(3), fcntl(2), fflush(3), malloc(3), memcmp(3), memcpy(3), memmove(3), memset(3), realloc(3), and strerror(3). In addition, the _D_b_:_:_g_e_t method may fail and throw a _D_b_E_x_- _c_e_p_t_i_o_n(3) or return _e_r_r_n_o for the following conditions: [EAGAIN] A lock was unavailable. [EINVAL] An invalid flag value or parameter was specified. The DB_THREAD flag was specified to the _D_b_:_:_o_p_e_n(3) method and neither the DB_DBT_MALLOC or DB_DBT_USER- MEM flags were set in the Dbt. A record number of 0 was specified. [EPERM] Database corruption was detected. All subsequent database calls (other than _D_b_:_:_c_l_o_s_e) will return EPERM. The _D_b_:_:_p_u_t method may fail and throw a _D_b_E_x_c_e_p_t_i_o_n(3) or return _e_r_r_n_o for any of the errors specified for the following DB and library functions: DbLock::get(3), DbLock::put(3), DbLockTab::id(3), DbLockTab::vec(3), DbLog::put(3), DbMpoolFile::get(3), DbMpoolFile::put(3), DbMpoolFile::set(3), calloc(3), fcntl(2), fflush(3), mal- loc(3), memcmp(3), memcpy(3), memmove(3), memset(3), real- loc(3), and strerror(3). In addition, the _D_b_:_:_p_u_t method may fail and throw a _D_b_E_x_- _c_e_p_t_i_o_n(3) or return _e_r_r_n_o for the following conditions: [EACCES] An attempt was made to modify a read-only database. [EAGAIN] A lock was unavailable. [EINVAL] An invalid flag value or parameter was specified. A record number of 0 was specified. An attempt was made to add a record to a fixed-length database that was too large to fit. An attempt was made to do a partial put. [EPERM] Database corruption was detected. All subsequent database calls (other than _D_b_:_:_c_l_o_s_e) will return EPERM. [ENOSPC] A btree exceeded the maximum btree depth (255). The _D_b_:_:_s_t_a_t method may fail and throw a _D_b_E_x_c_e_p_t_i_o_n(3) or return _e_r_r_n_o for any of the errors specified for the following DB and library functions: DbLock::get(3), DbLock::put(3), DbLockTab::id(3), DbLockTab::vec(3), DbM- poolFile::get(3), DbMpoolFile::put(3), calloc(3), fcntl(2), fflush(3), malloc(3), memcpy(3), and memset(3). The _D_b_:_:_s_y_n_c method may fail and throw a _D_b_E_x_c_e_p_t_i_o_n(3) or return _e_r_r_n_o for any of the errors specified for the following DB and library functions: Db::get(3), Db::sync(3), DbLock::get(3), DbLock::put(3), DbLock- Tab::id(3), DbLockTab::vec(3), DbLog::put(3), DbM- poolFile::get(3), DbMpoolFile::put(3), DbMpoolFile::set(3), DbMpoolFile::sync(3), calloc(3), close(2), fcntl(2), fflush(3), malloc(3), memcpy(3), mem- move(3), memset(3), munmap(2), open(2), realloc(3), str- error(3), unlink(2), and write(2). In addition, the _D_b_:_:_s_y_n_c method may fail and throw a _D_b_E_x_c_e_p_t_i_o_n(3) or return _e_r_r_n_o for the following condi- tions: [EINVAL] An invalid flag value or parameter was specified. [EPERM] Database corruption was detected. All subsequent database calls (other than _D_b_:_:_c_l_o_s_e) will return EPERM. SSEEEE AALLSSOO _T_h_e _U_b_i_q_u_i_t_o_u_s _B_-_t_r_e_e, Douglas Comer, ACM Comput. Surv. 11, 2 (June 1979), 121-138. _P_r_e_f_i_x _B_-_t_r_e_e_s, Bayer and Unterauer, ACM Transactions on Database Systems, Vol. 2, 1 (March 1977), 11-26. _T_h_e _A_r_t _o_f _C_o_m_p_u_t_e_r _P_r_o_g_r_a_m_m_i_n_g _V_o_l_. _3_: _S_o_r_t_i_n_g _a_n_d _S_e_a_r_c_h_i_n_g, D.E. Knuth, 1968, pp 471-480. _D_y_n_a_m_i_c _H_a_s_h _T_a_b_l_e_s, Per-Ake Larson, Communications of the ACM, April 1988. _A _N_e_w _H_a_s_h _P_a_c_k_a_g_e _f_o_r _U_N_I_X, Margo Seltzer, USENIX Pro- ceedings, Winter 1991. _D_o_c_u_m_e_n_t _P_r_o_c_e_s_s_i_n_g _i_n _a _R_e_l_a_t_i_o_n_a_l _D_a_t_a_b_a_s_e _S_y_s_t_e_m, Michael Stonebraker, Heidi Stettner, Joseph Kalash, Antonin Guttman, Nadene Lynn, Memorandum No. UCB/ERL M82/32, May 1982. _d_b___a_r_c_h_i_v_e(1), _d_b___c_h_e_c_k_p_o_i_n_t(1), _d_b___d_e_a_d_l_o_c_k(1), _d_b___d_u_m_p(1), _d_b___l_o_a_d(1), _d_b___r_e_c_o_v_e_r(1), _d_b___s_t_a_t(1), _d_b___i_n_t_r_o(3), _d_b___i_n_t_e_r_n_a_l(3), _d_b___t_h_r_e_a_d(3), _D_b(3), _D_b_c(3), _D_b_E_n_v(3), _D_b_E_x_c_e_p_t_i_o_n(3), _D_b_I_n_f_o(3), _D_b_L_o_c_k(3), _D_b_L_o_c_k_T_a_b(3), _D_b_L_o_g(3), _D_b_L_s_n(3), _D_b_M_p_o_o_l(3), _D_b_M_p_o_o_l_F_i_l_e(3), _D_b_t(3), _D_b_T_x_n(3), _D_b_T_x_n_M_g_r(3)