Scenario: i want to use SQLITE on embedded device with an eMMC instead of magnetic hard disk. All flash memories have a limited write cycles. All recent memories have a wear leveling system that allow to increase the lifetime of the memory. Each write is distribuited on the whole address space of the device (mapping between logical address and physical address). The main problem with a flash memory is the Write Amplification Factor (WAF): when you want to write some data into the memory the minimum amount of memory that will be written is the whole memory page (1, 2 or 4 KB depends on memory). So if you want to write 1 bit or 900 bytes you will write 1 page of 1 KB (example).
Suppose to have a SQLITE table with id (integer autoincrement), timestamp (integer indexed) and data (string not indexed).
It's possible to predict (overestimation) of the number of bytes written for each INSERT?
Scenario example: INSERT INTO table (timestamp,data) VALUES (140909090,"The data limited to 100 bytes").
Note that in my scenario normally the timestamp will increase because is the real timestamp of the datalogging.
It's possibile to predict that foreach insert 8 (id) + 8 (timestamp) + max 100 bytes (data) will be written for each insert. But what about the write overhead of id and timestamp indexes?
Related
This would be a noted one .
My data consists of few million records with fields like user agent , Ip addresses and so on consisting of 10 columns .Every time the unique strings are been mapped to integers before feeding into ML-Models for training and saved using pickle. The data is been passed incrementally and Dictionaries are been unpickled and used for the new data set mapping .
As the dictionary gets bulky , Im facing issues with RAM usage only at last 2 fields mentioned above.Could you suggest any alternative for this condition and why is there a spike though large memory is available.
Memory size - 64Gb
Input Dictionary is of the size 2GB
input file size around 5GB with lenght 32432769
I have created a database with one single table (check the code bellow). I plan to insert 10 rows per minute, which is about 52 million rows in ten years from now.
My question is, what can I expect in terms of database capacity and how long it will take to execute select query. Of course, I know you can not provide me an absolute values, but if you can give me any tips on change/speed rates, traps etc. I would be very glad.
I need to tell you, there will be 10 different observations (this is why I will insert ten rows per minute).
create table if not exists my_table (
date_observation default current_timestamp,
observation_name text,
value_1 real(20),
value_1_name text,
value_2 real(20),
value_2_name text,
value_3 real(20),
value_3_name text);
Database capacity exceeds known storage device capacity as per Limits In SQLite.
The more pertinent paragraphs are :-
Maximum Number Of Rows In A Table
The theoretical maximum number of rows in a table is 2^64
(18446744073709551616 or about 1.8e+19). This limit is unreachable
since the maximum database size of 140 terabytes will be reached
first. A 140 terabytes database can hold no more than approximately
1e+13 rows, and then only if there are no indices and if each row
contains very little data.
Maximum Database Size
Every database consists of one or more "pages". Within a single
database, every page is the same size, but different database can have
page sizes that are powers of two between 512 and 65536, inclusive.
The maximum size of a database file is 2147483646 pages. At the
maximum page size of 65536 bytes, this translates into a maximum
database size of approximately 1.4e+14 bytes (140 terabytes, or 128
tebibytes, or 140,000 gigabytes or 128,000 gibibytes).
This particular upper bound is untested since the developers do not
have access to hardware capable of reaching this limit. However, tests
do verify that SQLite behaves correctly and sanely when a database
reaches the maximum file size of the underlying filesystem (which is
usually much less than the maximum theoretical database size) and when
a database is unable to grow due to disk space exhaustion.
Speed determination has many aspects and is thus not a simple how fast will it go, like a car. The file system, the memory, optimisation are all factors that need to be taken into consideration. As such the answer is the same as the length of the anecdotal piece of string.
Note 18446744073709551616 is if you utilise negative numbers otherwise the more frequently mentioned number of 9223372036854775807 is the limit (i.e a 64 bit signed integer)
To utilise negative rowid numbers and therefore the higher range you have to insert at least 1 negative value explicitly into a rowid or alias thereof as per If no negative ROWID values are inserted explicitly, then automatically generated ROWID values will always be greater than zero.
I want to build a 20,000,000 record table in sqlite, but the file size is slightly larger than its TAB-separated plaintext representation.
What are the ways to optimize data size storage, specific to sqlite?
Details:
Each record has:
8 integers
3 enums (represented for now as 1 byte text),
7 text
I suspect that the numbers are not stored efficiently (value range 10,000,000 to 900,000,000)
According to the docs, I expect them to take 3-4 bytes, if stored as a number, and 8-9 bytes if stored as text (maybe additional termination byte or size indicator byte), meaning 1:2 ratio between storing as int : store as text).
But it doesn't appear so.
Your integers should take at least 3-4 bytes (3 Bytes for up to 2^24 =~ 16,000,000). Additionally SQLite always stores at least one byte for every column as size information (also for your 1 byte texts --> 2bytes in sum for each).
Some questions:
Do you use a compound primary key or a primary key other than a plain integer?
Do you use other indexes?
Did you try to vacuum the database? (command "vacuum") -- a SQLite database is not necessarily auto-vacuum't, so when data is deleted, the space stays reserved.
One further:
Do you already have your 20,000,000 entries or less? For small databases the storage overhead can be much larger than the real content size.
There's an SQLite database being used to store static-sized data in a round-robin fashion.
For example, 100 days of data are stored. On day 101, day 1 is deleted and then day 101 is inserted.
The number of rows is the same between days. The the individual fields in the rows are all integers (32-bit or less) and timestamps.
The database is stored on an SD card with poor I/O speed,
something like a read speed of 30 MB/s.
VACUUM is not allowed because it can introduce a wait of several seconds
and the writers to that database can't be allowed to wait for write access.
So the concern is fragmentation, because I'm inserting and deleting records constantly
without VACUUMing.
But since I'm deleting/inserting the same set of rows each day,
will the data get fragmented?
Is SQLite fitting day 101's data in day 1's freed pages?
And although the set of rows is the same,
the integers may be 1 byte day and then 4 bytes another.
The database also has several indexes, and I'm unsure where they're stored
and if they interfere with the perfect pattern of freeing pages and then re-using them.
(SQLite is the only technology that can be used. Can't switch to a TSDB/RRDtool, etc.)
SQLite will reuse free pages, so you will get fragmentation (if you delete so much data that entire pages become free).
However, SD cards are likely to have a flash translation layer, which introduces fragmentation whenever you write to some random sector.
Whether the first kind of fragmentation is noticeable depends on the hardware, and on the software's access pattern.
It is not possible to make useful predictions about that; you have to measure it.
In theory, WAL mode is append-only, and thus easier on the flash device.
However, checkpoints would be nearly as bad as VACUUMs.
I have read their limits FAQ, they talk about many limits except limit of the whole database.
This is fairly easy to deduce from the implementation limits page:
An SQLite database file is organized as pages. The size of each page is a power of 2 between 512 and SQLITE_MAX_PAGE_SIZE. The default value for SQLITE_MAX_PAGE_SIZE is 32768.
...
The SQLITE_MAX_PAGE_COUNT parameter, which is normally set to 1073741823, is the maximum number of pages allowed in a single database file. An attempt to insert new data that would cause the database file to grow larger than this will return SQLITE_FULL.
So we have 32768 * 1073741823, which is 35,184,372,056,064 (35 trillion bytes)!
You can modify SQLITE_MAX_PAGE_COUNT or SQLITE_MAX_PAGE_SIZE in the source, but this of course will require a custom build of SQLite for your application. As far as I'm aware, there's no way to set a limit programmatically other than at compile time (but I'd be happy to be proven wrong).
It has new limits, now the database size limit is 256TB:
Every database consists of one or more "pages". Within a single database, every page is the same size, but different databases can have page sizes that are powers of two between 512 and 65536, inclusive. The maximum size of a database file is 4294967294 pages. At the maximum page size of 65536 bytes, this translates into a maximum database size of approximately 1.4e+14 bytes (281 terabytes, or 256 tebibytes, or 281474 gigabytes or 256,000 gibibytes).
This particular upper bound is untested since the developers do not have access to hardware capable of reaching this limit. However, tests do verify that SQLite behaves correctly and sanely when a database reaches the maximum file size of the underlying filesystem (which is usually much less than the maximum theoretical database size) and when a database is unable to grow due to disk space exhaustion.
The new limit is 281 terabytes. https://www.sqlite.org/limits.html
Though this is an old question, but let me share my findings for people who reach this question.
Although Sqlite documentation states that maximum size of database file is ~140 terabytes but your OS imposes its own restrictions on maximum file size for any type of file.
For e.g. if you are using FAT32 disk on Windows, maximum file size that I could achieve for sqLite db file was 2GB. (According to Microsoft site, limit on FAT 32 system is 4GB but still my sqlite db size was restricted to 2GB). While on Linux , I was able to reach 3 GB (where I stopped. it could have reached more size)
NOTE: I had written a small java program that will start populating sqlite db from 0 rows and go on populating until stop command is given.
The maximum number of bytes in a string or BLOB in SQLite is defined by the preprocessor macro SQLITE_MAX_LENGTH. The default value of this macro is 1 billion (1 thousand million or 1,000,000,000).
The current implementation will only support a string or BLOB length up to 231-1 or 2147483647
The default setting for SQLITE_MAX_COLUMN is 2000. You can change it at compile time to values as large as 32767. On the other hand, many experienced database designers will argue that a well-normalized database will never need more than 100 columns in a table.
SQLite does not support joins containing more than 64 tables.
The theoretical maximum number of rows in a table is 2^64 (18446744073709551616 or about 1.8e+19). This limit is unreachable since the maximum database size of 140 terabytes will be reached first.
Max size of DB : 140 terabytes
Please check URL for more info : https://www.sqlite.org/limits.html
I'm just starting to explore SQLite for a project I'm working on, but it seems to me that the effective size of a database is actually more flexible than the file system would seem to allow.
By utilizing the 'attach' capability, a database could be compiled that would exceed the file system's max file size by up to 125 times... so a FAT32 effective limit would actually be 500GB (125 x 4GB)... if the data could be balanced perfectly between the various files.