DRMS_RecordSet_t * drms_open_recordset ( DRMS_Env_t env,
const char *  rsquery,
int *  status 
)

Retrieve a set of records specified by a recordset query. Within the current DRMS session (whose information is stored in env), this function submits a database query specified in recordsetname and creates a record-set structure (DRMS_RecordSet_t) to contain the results of the query. If, at the time this function is called, a requested record structure (DRMS_Record_t) exists in the record cache (env->record_cache), then a pointer to that record structure is inserted into the results record set. Otherwise, a new record struc- ture is created, populated from the database, inserted into the record cache, and inserted into the results record set. The newly created record is marked read-only and assigned a permanent lifetime (DRMS_PER- MANENT).

Upon successful completion, the function returns a DRMS_RecordSet_t pointer, and sets *status to DRMS_SUCCESS. If an error occurs, the function returns NULL and sets *status to an appropriate error code defined in drms_statuscodes.h. Typical errors are as follows. If a problem occurs during communication with the database server, *status is set to DRMS_ERROR_QUERYFAILED.

The caller owns the allocated memory associated with the returned record set and must release it by calling drms_close_records.

The main difference between this function and drms_open_records is that the former creates a DRMS_RecordSet_t structure for each record specified by the record-set query. But the current function creates a DRMS_RecordSet_t structure for each member of the current subset (or 'chunk') of the records specified by the record-set query. Only one chunk of records resides in memory at any time. When a record in a non-resident chunk is needed, the current chunk of DRMS_RecordSet_t structures is freed, and the next chunk is loaded into memory. The purpose of this function is to conserve memory by facilitating the processing of chunks of records instead of processing the entire set of records. To override the default chunk size, the user calls drms_recordset_setchunksize.

Operating on chunks of records is transparent to the caller who can continue to interate through records without being cognizant of 'chunking'. To iterate through all records in the set, after calling this function, the caller would call drms_recordset_fetchnext in a loop to obtain a pointer to each record in the sequence. When drms_recordset_fetchnext returns NULL, no more records remain in the record-set.

Parameters:
env DRMS session information.
rsquery A string that specifies a database query. It includes a series name and clauses to extract a subset of records from that series. Please see http://jsoc.stanford.edu/jsocwiki/DrmsNames for more information about database queries.
status Pointer to DRMS status (see drms_statuscodes.h) returned by reference. 0 if successful, non-0 otherwise.
Returns:
The set of records retrieved by the query.
Examples:
drms_record_ex6.c.

Definition at line 13517 of file drms_record.c.


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