Index sequential file The file includes a number of indexes and the computer can look at these to find exactly where in the file to find the record - in much the same way that you Jun 6, 2024 · Indexed Sequential Access Method (ISAM) is a special file organization solution that is implemented in database systems for the purpose of data retrieval acceleration and process optimization. • Primary index (clustering index) – Index on the search key • Dense index – (key, pointer) pair for every record • Find the key from index and follow pointer – Maybe through binary search • Q: Why dense index? – Isn’t binary search on the file the same? 20 10 40 30 60 50 80 70 100 90 Dense Index 10 20 30 40 50 60 70 80 90 100 Nov 1, 2011 · Indexed sequential file Each record of a file has a key field which uniquely identifies that record. File Organisation Model # 4. An index sequential file with two indexes. 3. The Indexed Sequential Access Method (ISAM) allows programs to directly access specific items in large data files. In addition, each record in these files is preceded by a 2 or 4 byte record header. A file organization where the records can be accessed directly as well as sequentially is called indexed sequential file. May 4, 2015 · 3. Advantages: Sequential file organization in DBMS is the simplest of all file organization methods. Variable-length records save disk space. Here records are stored in order of primary key in the file. It consists of two parts: Data File contains records in sequential scheme. In the case of large volumes of data, this method is efficient in terms of speed as access to the data is relatively fast in this method. Line-sequential files are sequential files that reside on the hierarchical file system (HFS) and that contain only characters as data. Following are the key attributes of sequential Record sequential files are nearly always simply called sequential files, since record sequential is the default for a sequential file. [2] The construction of a hierarchy of indexes (the indexed sequential access method) is one means of providing rapid random access to sequential files. I'm thinking of storing the results in a simple database but the problem is the database needs to available on a number of Unix platform for the program to work. For each primary key, the value of the index is generated and mapped with the record. An index file contains key-value pairs where the key is used to locate the corresponding value quickly, allowing for faster data retrieval but potentially slower writing operations. The easiest method for file Organization is the Sequential method. Records in a record sequential file can be either fixed or variable in length. Line-sequential file organization. According to IBM, the system lists files or data in a pre-determined order. In this records are stored randomly on a direct access device such as magnetic disk by a primary key. For each primary key, an index value is created and mapped to the record. Index is a sequential file Mar 10, 2021 · What is indexed sequential organization? Indexed Sequential File Organization An indexed sequential file consists of records that can be accessed sequentially. In ISAM, data is stored in sorted order based on a key, and an index is maintained to facilitate quick search operations. The capability of directly accessing a record based on a key can only be achieved if the external storage device supports this type of access i. PART 5: Comparisions of Sequential, Index Sequential & Direct Access File Organization: https://youtu. The Indexed file can be accessed sequentially same as Sequential file organization as well as randomly only if the RECORD-KEY is known. In this article, we will learn about sequential file organization and its advantages Sep 29, 2020 · Serial files are quite limiting, but are useful for simple data sets and configuration files. Apr 26, 2024 · A sequential file stores data in a linear, sequential order for efficient reading and writing operations. e. Dibanding Sequential file, pemanggilan data menjadi lebih cepat. be/IDSOOL3iiigPART 4: Cluster File Organization: https: AspecificrecordoftheSTUDENTtype: STUDENT(9901536,“JamesBond”,“1BondStreet,London”,“IntelligentSer-vices”,9) Fixed-lengthandvariable-lengthrecordsinfiles Indexed Sequential Access Method (ISAM) is a method for creating, maintaining, and manipulating computer files of data so that records can be retrieved sequentially or randomly by one or more keys. An indexed file is a file whose default access path is built on key values. The gradual performance deterioration caused by deletions from and insertions into an index-sequential file after loading is analyzed. The organization of a file can be sequential, indexed, or relative (discussed in another section). We have also listed their indexing methods to store the data for these organization mechanisms. The inclusion of indexes means that additional space is needed to store these data structures alongside the actual data records. There are many applications that can benefit from the use of variable-length records. Index ini diakhiri denga adanya suatu pointer (penunjuk) yang bisa menunjukkan secara jelas posisi data yang selengkapnya. Load the entire index file into main memory. (Thus, order of data recs is `close to’, but not identical to, the sort order. IBM supports indexed files with the Indexed Sequential Access Method on OS/360 and successors. Main / Primary File (File Utama) 2. Indexed sequential access method (ISAM) ISAM method is an advanced sequential file organization. The direct file organization, like the indexed sequential file organiza- tion, contains information which is stored in the file according to a key. Also, there is a clear difference between updating a sequential file and updating an indexed file. This chapter discusses the concept of files and their methods of organization, for example, heap or pile files, sequential files, indexed sequential files and direct files. An indexed sequential file consists of records that can be accessed sequentially. As is shown in Figure 2. Indexed sequential access method is the organization of file in an advanced sequential manner. It employs an index, which is a separate data structure containing pointers to the records, allowing for efficient searching and retrieval. Sep 7, 2021 · In the case of Indexed files two types of files are created: Data file: It consists of the records in sequential order. Each index defines a different ordering of the records. A primary key is used in this method to store records in the file. Sequential File Organization. Indexed sequential access file organization Indexed sequential access file is a combination of both sequential file and direct access file organization. 1 On hard drives at least. The indexed file consists of two files – data file and index file. idx extension to An index-sequential file in COBOL can briefly be described as a file with at least one key concept. An index value is generated for each primary key and mapped with the record. Other types of files include: sequential files where order of the data is maintained, index sequential files for large data sets and random files which allow you to access any item without searching through the file from the start. Indexed files, record sequential files with variable length records and relative files with variable length records all contain file headers. In addition, each record in these files is preceded by a two- or four-byte record header. Records in sequential files can be read or written only sequentially. In this, the indices are based on a sorted ordering of the values. It has less storage space as compared to sequential file. Indexed File Organization. Each record ends with a newline character. May 17, 2023 · Types of File Organization Mechanism. As M approaches N, the full table scan wins. Key Words and Phrases: ISAM, index sequential, The final sequential search will take only up to 10000 comparisons because the blocks being pointed to are now blocks of 10000 memory addresses! We have gone from having to search 100000000 records, to 1000100 records to 10200 records! An index sequential file with two indexes. Fixed length KSDS (MATEPK. Kerugian Index Sequential File Access (pemanggilan) data tidak bisa disamakan dengan random (direct access file). File Organization Comparison of sequential and indexed sequential Example: a file contains 1 million records On average 500,000 accesses are required to find a The algorithm used for searching an indexed sequential file is simple and straight. The elements in the index, as well as elements in the file, must be sorted on the file. open input xyzfile My question is: Is there somehow a possibility to put the name "xyzfile" in variable an write instead. Mar 4, 2022 · Indexed Sequential File Organization: Direct access of a record was not possible with Sequential organization, to overcome this Indexed Sequential file organization is used. Dec 20, 2023 · The Indexed Sequential Access Method (ISAM) is a file management system used in computing to enable quick access to records in a large sequential file. Apr 21, 2020 · PART 5: Comparisions of Sequential, Index Sequential & Direct Access File Organization: https://youtu. 2. Indexed-sequential file refers to a file in which data are stored in a sequence (similar to the sequential method), but in addition an index is created that shows the memory address of each piece of data. Aug 26, 2012 · The format of the file may be optimized for one kind of access or the other, for example text is typically "sequential" while database files tend to be highly "random". Solution: treat index kept on disk as a sequential file and construct a sparse index on it. When you update a sequential file, you rewrite the entire file; this practice leaves the original file as a convenient backup in case the job must be rerun. Indexed file organization. Two file organizations often proposed for these processing requirements are indexed sequential and direct. File organization is INDEXED and accessing mode should be SEQUENTIAL. An examination is made of the consequences of partially or completely replacing one or more index levels Berkas index sequential adalah metode penyimpanan data yang mengintegrasikan prinsip penyimpanan data sekuensial dengan penggunaan indeks untuk meningkatkan efisiensi pencarian dan akses data. INTRODUCTION A familiar problem in database and file design is choosing between a B+ tree and an indexed sequential implementation for a file. Data File contains records in sequential scheme. be/IDSOOL3iiigPART 4: Cluster File Organization: https: Jun 6, 2024 · Can Sequential file Organization be used for streaming data processing? Yes, Sequential file Organization is appropriate for streaming data processing where data comes in continually and sequentially. move "xyzfile" to var-file open input var-file Thanks alot in advance An Indexed Sequential File is organised so that it is easy to find information quickly without the computer having to search through the whole file. This index contains the address of the record in the file. Data entries direct search for (Index File) (Data Index Sequential File merupakan perpaduan terbaik dari teknik sequential dan random file. THE INDEXED SEQUENTIAL FILE A file management system that allows records to be accessed either sequentially (in the order they were entered) or randomly (with an index) A secondary set of hash tables known as indexes is created that contains pointers to the main file In indexed sequential file, records are organized in sequence based on key fields Each file has an index to support random A file header is a block of 128 bytes at the start of the file. Let kindex be an array of the keys in the index, and let pindex be the array of pointers within the index to the actual records in the file, and the size of index is also taken in a variable. C[index] is things like loading the index, looking up a key, and reading the row IDs. Indexed file organization stores the record sequentially depending on the value of the RECORD-KEY(generally in ascending order). Files stored on tapes are actually physically sequential, but tapes are typically only used for archiving and you are unlikely to deal with them 4. The model developed assumes that overflow records are handled by chaining. Nov 7, 2023 · Sequential File Organization or Ordered Index File. The process that is used is essentially the same as that described for sequential file input. me/gatecselecturesbyamitkhurana 📍I will cover entire 'GATE CS-IT' syllabus and make videos🎥 of eac Dec 28, 2024 · Clustered File Organization; ISAM (Indexed Sequential Access Method) We will be discussing each of the file Organizations in further sets of this article along with the differences and advantages/ disadvantages of each file Organization method. Indexes of key fields are maintained to achieve fast retrieval of required file records in indexed files . can process indexed files as if they were sequential files. The organization of an indexed sequential file combines the positives aspects of both the sequential and the direct access files. Note that the cost of using the index isn't really constant. Hence, indexed files are often called indexed sequential files. An indexed sequential file stores Most types of indexed file actually comprise two separate files: the data file (containing the record data) and the index file (containing the index structure). In the case of Indexed files two types of Jun 30, 2022 · Indexed sequential access method also known as ISAM method, is an upgrade to the conventional sequential file organization method. – The sequential file – The indexed sequential file – The indexed file – The direct, or hashed, file The Pile • Least complicated form of file organization • Data are collected in the order they arrive • Each record consists of one burst of data • Purpose is simply to accumulate the mass of data and save it Mar 6, 2023 · Indexed Sequential Access. A RECORD-KEY in an Indexed file is a variable that must be part of the record/data. In this case, records are stored in the file with the help of the primary key. Setiap entry pada indeks mempunyai bentuk (nilai key Indexed Sequential File Organization An indexed sequential file consists of records that can be accessed sequentially. Indexed sequential access file combines both sequential file and direct access file organization. Indexed Sequential File Structured dengan B-Tree Pada gambar tersebut ada N blok data dan 3 tingkat dari indeks. Mar 31, 2015 · Model dasar organisasi berkas/file terdiri atas 3 macam, yaitu: Sequential File, Random File, dan Indexed Sequential File (Noersasongko dan Andoko, 2010). KSDS) file is used as an input file and trying to read all the records sequentially. Each record in Each element in the index table consists of a key Kindex and pointer to the record in the field that corresponds to the kindex. An indexed sequential access method is a static, hierarchical, disk-based index structure that enables both (single-dimensional) range and membership queries on an ordered data file. The order of the records is fixed. Overflow Area Indeks dan Parameter Indeks Indeks berisi pasangan nilai atribut dengan pointer acuan, file indeks adalah kumpulan Index Sequential File merupakan perpaduan terbaik dari teknik Sequential dan random file. May 27, 2013 · 8. Indexed file organization is a type of file organization used in database management systems (DBMS) where data is stored in a file or table with an index. • To build a clustered index, first sort the Heap file (with some free space on each page for future inserts). Using hashed overflow, the time to locate a record is dependent not on the total volume of over- flow records as in conventional ISAM, but on the per- centage use of space dedicated to overflow records. com Mar 11, 2024 · The full form of ISAM is Indexed Sequential Access Method. • outer index – a sparse index of the basic index • inner index – the basic index file If even outer index is too large to fit in main memory, yet another level of index can be created, and so on. It employs a similar key-index idea, in which the primary key is utilised to sort the records. Sequential files allow for efficient access to data only if there is a efficient way to determine where the d ata is stored given a key. com/file/d/1KAWEpApAhaae2VWJEDS5jdZBwQGPfIev/view?usp=drivesdkIf you have any doubts then you can connect me viaGmail : exa A sequential file contains records organized by the order in which they were entered. And leaf node will have lowest level of data. Let r, k and key be defined as before. Indeks 3. He often would like to design a file so that sequential and random processing can both be performed efficiently. The key fields identify the records in an indexed file. The physical organization of the files is designed and ordered by the File Manager of the operating system. Jul 8, 2017 · Index Sequential File merupakan perpaduan terbaik dari teknik Sequential dan random file. An analytic method for comparing the performance of B+ trees and indexed sequential files is proposed. The index is searched 1st then the array and guides the search in the array. Indexed file organization Each record in the file A file header is a block of 128 bytes at the start of the file. • Overflow pages may be needed for inserts. File reading starts from the first record and continue till the end of the file. Further, in most indexed file implementations, within the data area the records are stored in ascending order of primary key. Sequential file organization is a common tool used by log processing and real-time analytics systems to handle streaming data efficiently. An indexed file is identified by the ORGANIZATION IS INDEXED clause of the SELECT statement. sorted into order of a key field) which has an index . Also, it generates an index value, and mapping is done with the record. Following are the key attributes of Jun 22, 2013 · Get Codes for C, C++, JAVA, C#, HTML and JavaScript and knowledge about Online Marketing,SEO,Web Hosting,Blogging Tips and much more B+. It uses the same concept of key-index where the primary key is used to sort the records. Analysis of Index-Sequential Files * 673 The keys of the records in the file and of the records inserted are modeled as being randomly drawn from an underlying distribution. Direct access is also possible. An index sequential file with three index levels index structure is stored in a single file, the information th ere is broken into disk blocks. The indexed sequential search Indexed Sequential Access Method (ISAM) is a file organization technique that provides efficient ways to both sequentially and randomly access records. The B+ tree file organization is a very advanced method of an indexed sequential access mechanism. When an indexed file is read in sequential access mode, the record made available by the READ statement is determined as follows: . Thus, the file is physically a sequential file onto which one or more index structures have been superimposed. Jul 6, 2022 · Let's see the advantages and disadvantages of using the Sequential file organization method in a DBMS. Index File contains the primary key and its address in the data file. The only access (record transmission) mode allowed for line-sequential files is sequential. 03 alex 02 juancho 01 homer ----(index) Id (It means, I've to read the file by Id, ascendant way) My question is the next one, how make an structure that index the file to read it according to the index? (or key, in this case i'd be the Id) If you can, drop some example in java Line-sequential file organization Line-sequential files are sequential files that reside in the z/OS® UNIX file system and that contain only characters as data. IBM virtual storage operating systems added VSAM, which supports indexed files as Key Sequenced Data Sets (KSDS), with more options. ) Index entries . B tree index file is similar to B+ tree index files, but it uses binary search concepts. The algorithm used for searching an indexed sequential file is simple and straight. Started by IBM in the 1960s, also known as the Indexed Sequential Access Method, or ISAM, this method of data storage allowed both sequential and random Jul 25, 2023 · Another disadvantage of indexed sequential files is the higher storage requirements compared to other file organization methods. It is an efficient file organization method that stores data sequentially while also maintaining secondary indexes. These Ordered or Sequential file organizations might store the data in a dense or sparse format. Using the primary key, the records are sorted. So far in COBOL, we have been using files with sequential organization. Unlike the indexed sequential file organization, the information is not neces- sarily stored in a sequential order. These ordered or sequential file organizations can store data in a dense or sparse format − Apr 22, 2023 · A comparison of the capabilities of sequential files with the other two types of files can be seen in Figure 1. data records are stored in a Heap file. This can be quite variable depending on B+ File Organization. 2. It uses a tree-like structure to store records in File. File urut berindeks (indexed sequential file) atau sering disebut dengan ISAM (indexed sequential access method) merupakan file dengan organisasi urut (sequential Indexed sequential files similar to sequential files, but contain two added features: False (T/F) Reliability problems can occur when the disk allocation table and file allocation table are stored on disk. Due to the lack of organized sorting, sequential files have a high average search time. When you create a file, the system either has to insert the new file in the proper sequence or re-index the whole file list. Indexed sequential access file organization. There are two types of file organization mechanism as given below. The data file is created just like a sequential file, but it can also be accessed randomly. We will consider the following categories of index structures: • Indexes on Sequential Files. Indexed Sequential Access Method (ISAM) This is an advanced sequential file organization method. You can say that it is an C. Since ISAM is static, it does not change its structure if records Indexed files An index file is made of a data file, which is a sequential file, and an index. What are the components of sequential file? The indexed sequential file architecture comprises three components which includes the main file where the records are stored sequentially, an index allowing quick Indexed Sequential Files -Introduction An Indexed Sequential File is organised so that it is easy to find infonnation quickly without the computer having to search through the whole file. This file have multiple keys, An index consists of keys and addresses. Feb 27, 2024 · Sequential file organization is the simplest type of file organization, where files are stored one after the other, rather than storing different files in rows and columns (in a tabular form), storing data in rows. If search key does not correspond to primary key (of a relation), then multiple records can have the same search key value Dense Index Files: index entry appears for every search key value in the record le. B Tree index Files. INDEXED FILE ORGANIZATIONS Apr 25, 2020 · There are 2 types of sequential files- A line sequential file, Record sequential file. , records in the le are not ordered according to secondary index). Are there any (simple) databases which can be found on any Unix platforms? Or should I use some sort of index-sequential file? Jun 26, 2014 · I have a file and an index: for example: (the file) ----Id number. magnetic drums and disks. Jan 24, 2022 · The file access methods provide operations like reading from or writing to a file stored in the computer memory. Indexed sequential access is a combination of sequential and direct access methods, which uses an index file to provide direct access to specific records within a file. Oct 9, 2020 · 📍 Telegram channel link(for NOTES and DOUBTS) https://t. EMPL. Each element in the index points to a block of elements in the array or another expanded index. 1 Struktur Pohon Sebuah pohon (tree) adalah struktur dari sekumpulan elemen, dengan salah satu elemennya merupakan akarnya atau root dan sisanya yang lain merupakan bagianbagian pohon yang terorganisasi dalam susunan berhirarki dengan root sebagai puncaknya. A full index to a file is one in which there is an entry for every record. Preliminary results indicate that indexed sequential files may be more efficient than B+ trees in certain applications. Mar 24, 2023 · To improve the efficiency of accessing data in a sequential file, various techniques like buffering, caching, and memory-mapped files can be used. The index value is generated for each primary key and mapped to the record. May 15, 2024 · A sequential file can be stored on a sequential access device such as magnetic tape or on a direct access device such as magnetic disk. magnetic disk and data is accessible either randomly or sequentially. A computer systems designer is faced with a decision concerning the organization of data files. Pada makalah ini akan dibahas mengenai organisasi berkas indexed sequential. Since this is the default, no clauses were needed in the select file. indexed file is typically a master file. Indexed sequential files solve this problem but at a cost of organizational simplicity. ISFs offer a blend of direct and sequential access to records, making them suitable for environments that require frequent data retrievals and modifications. Sparse Index Files: only index One of the advantages of an Indexed Sequential File is that it is possible to find the required record, read it, alter it, and write the altered record back into position. Indexed Sequential File Organization. Indexed Sequential Access File Organisation: The retrieval of a record from a sequential file, on average, requires access to half the records in the file, making such enquiries not only I inefficient but very time consuming for large files. A key can be used to establish unique information and to retrieve the data in an ordered way. trees and indexed sequential files is proposed. Mar 24, 2010 · where attribute 2 may be optional. An indexed sequential file is a sequential file (i. In indexed sequential access file, records are stored randomly on a direct access device such as magnetic disk by a primary key. The indexes that makes this possible is maintained by the runtime system, so the programmer only have to declare the file and supply the data. Vision is ACUCOBOL-GT's native indexed sequential file system. Keuntungan Index Sequential File Sangat cocok untuk digunakan menyimpan batch data ataupun individual data. It consists of two parts − Data File contains records in sequential scheme. Index files are also called key files, so the access method is also known as the Keyed Sequential Access Method (KSAM). Indexed Sequential File. Index file: It consists of the RECORD-KEY and the address of the RECORD-KEY in the data file. In File, records are stored in a tree-like structure. These indexes enable both sequential and random access, making it more versatile and better than sequential file organization. An index consists of keys and addresses . After you place a record into a sequential file, you cannot shorten, lengthen, or delete the record. 1. An analytic method for comparing the performance of B+ trees and indexed sequential files is proposed and preliminary results indicate that indexed Sequential files may be more efficient than B- trees in certain applications. File index sequential ditujukan untuk keperluan akses data secara langsung dan juga sequential. May 6, 2016 · When I want to open an index-sequential file I write. On the other hand, indexed sequential files combine the benefits of sequential and indexed file organizations. The access can be done either automatically (JOB INPUT) or controlled (GET). the sequential order of the le (i. Where this is the case, the name that you specify in your COBOL program is given to the data file and the name of the associated index file is produced by adding an . See full list on baeldung. However, in this method also, records will be sorted. The index is a of the file in the index as opposed to the sequen- tial mode. To access a record in the file : 1. 3 Kerugian Index Sequential File Access (pemanggilan) data tidak bisa disamakan dengan random (direct access file). 5. Feb 27, 2023 · In Indexed Sequential Search a sorted index is set aside in addition to the array. Support for indexed files is built into COBOL [1] and PL/I. If the file position indicator was set by the processing of a START or OPEN statement, the record pointed to is made available if it is still accessible through the path indicated by the current record pointer. What is Indexed Sequential File? An Indexed Sequential File (ISF) is a data storage system widely used in maintaining large databases. File urut (sequential file) merupakan file dengan organisasi urut (sequential organization) dengan pengaksesan secara urut (s equential access). In an indexed sequential file, records are stored sequentially on a direct access device ( i. Sequential File Organization or Ordered Index File. This method allows users to access any part of a file directly while maintaining the sequential order of the data. indexed sequential file A file combining properties of random-access files and sequential files. This index is nothing but the address of record in the file. ISAM (Indexed Sequential Access Method) is a file management system developed at IBM in the 1960s to access records either sequentially, in the order they were entered or randomly with an index. The records of the data file are stored in sequential order according to some data attribute(s). Formulas for computing the expected number Apr 26, 2019 · Index Sequential File merupakan perpaduan terbaik dari teknik sequential dan random file. Sequential File 6 Index Sequential File 2. google. For each primary key, an index value is generated and mapped with the record. 2 Contoh dari indexed sequential 2. Index – a small file with only two fields: The key of the sequential file The address of the corresponding record on the disk. In this method, each root will branch to only two nodes and each intermediary node will also have the data. It provides fast, flexible, and reliable data storage to ACUCOBOL-GT applications in all environments except VMS where ACUCOBOL-GT uses the native RMS file system. Nov 29, 2023 · In the worst situation, the system may need to traverse the entire file, which is inefficient for huge files. D. Teknik penyimpanan yang dilakukan, menggunakan suatu index yang isinya berupa bagian dari data yang sudah tersortir. In addition to a data file, ISAM requires at least one index . 2011). Dense Index Notes link : https://drive. 2 Keuntungan Index Sequential File Sangat cocok untuk digunakan menyimpan batch data ataupun individual data. One way to create a keyed access path for an indexed file is by using DDS. Search the index file to find the ISAM (Indexed sequential access method) is an advanced sequential file organization method. Struktur organisasi ini menggunakan node-node indeks dan pointer untuk mengatur data secara hierarkis dan memandu pencarian secara efisien. These are generally fast and a more traditional type of storing mechanism. B+ tree file organization is the advanced method of an indexed sequential access method. It consists of two parts −. An index sequential file with three index levels There is nothing stopping us adding a further index! Once we have got to the place where all accounts begin with 4584, we can check the next two digits by searching from that point sequentially. VSAM was designed to ensure efficient sequential processing (large transfers with few seeks), and is capable of delivering this even after record Jan 1, 2018 · An indexed sequential access method is a static, hierarchical, disk-based index structure that enables both (single-dimensional) range and membership queries on an ordered data file. The various file access methods are, Sequential Access Method; Direct Access Method; Indexed Access Method; Indexed Sequential Access Method. Struktur file index sequential Komponen file index sequential, yaitu : 1. In this method, records are stored in the file using the primary key. Preliminary results indicate that indexed sequential files may be . , Topi, H. 2, the key of Jan 24, 2020 · # Indexed query C[index] + (C[random] * M) # Full table scan C[sequential] * N When M << N the indexed query wins. The maintenance of index files therefore can be very time consuming. “Because of their inflexibility, sequential files are not used in a database but may be used for files that back up data from a database” (Venkataraman, R. While indexed sequential files have some unique requirements, almost all modern file systems are designed to mitigate the unique performance characteristics of movable head rotating magnetic media. 3. Source for information on indexed sequential file: A Dictionary of Computing dictionary.