A library that provides an embeddable, persistent key-value store for fast storage.
45828c7215
Summary:
Hello and thank you for RocksDB,
While looking into the buffered io used when an `OPTIONS` file is read I noticed the `OPTIONS` files produced by RocksDB 5.8.8 (and head of master) were just over 4096 bytes in size, resulting in the version of glibc I am using (glibc-2.17-196.el7) (on the filesystem used) being passed a 4K buffer for the `fread_unlocked` call and 2 system call reads using a 4096 buffer being used to read the contents of the `OPTIONS` file.
If the buffer size is increased to 8192 then 1 system call read is used to read the contents.
As I think the buffer size is just used for reading `OPTIONS` files, and I thought it likely that `OPTIONS` files have increased in size (as more options are added), I thought I would suggest an increase.
[ If the comments from the top of the `OPTIONS` file are removed, and white space from the start of lines is removed then the size can be reduced to be under 4K, but as more options are added the size seems likely to grow again. ]
Create a new database:
```
> ./ldb --create_if_missing --db=/tmp/rdb_tmp put 1 1
OK
```
The OPTIONS file is 4252 bytes:
```
> stat /tmp/rdb_tmp/OPTIONS* | head -n 2
File: ‘/tmp/rdb_tmp/OPTIONS-000005’
Size: 4252 Blocks: 16 IO Block: 4096 regular file
```
Before, the 4096 byte buffer is used from 2 system read calls:
```
> strace -f ./ldb --try_load_options --db=/tmp/rdb_tmp get DOES_NOT_EXIST 2>&1 |
grep -A 1 'RocksDB option file'
read(3, "# This is a RocksDB option file."..., 4096) = 4096
read(3, "e\n metadata_block_size=4096\n c"..., 4096) = 156
```
ltrace shows 4096 passed to fread_unlocked
```
> ltrace -S -f ./ldb --try_load_options --db=/tmp/rdb_tmp get DOES_NOT_EXIST 2>&1 |
grep -C 3 'RocksDB option file'
[pid 51013] fread_unlocked(0x7ffd5fbf2d50, 1, 4096, 0x7fd2e084e780 <unfinished ...>
[pid 51013] fstat@SYS(3, 0x7ffd5fbf28f0) = 0
[pid 51013] mmap@SYS(nil, 4096, 3, 34, -1, 0) = 0x7fd2e318c000
[pid 51013] read@SYS(3, "# This is a RocksDB option file."..., 4096) = 4096
[pid 51013] <... fread_unlocked resumed> ) = 4096
...
```
After, the 8192 byte buffer is used from 1 system read call:
```
> strace -f ./ldb --try_load_options --db=/tmp/rdb_tmp get DOES_NOT_EXIST 2>&1 | grep -A 1 'RocksDB option file'
read(3, "# This is a RocksDB option file."..., 8192) = 4252
read(3, "", 4096) = 0
```
ltrace shows 8192 passed to fread_unlocked
```
> ltrace -S -f ./ldb --try_load_options --db=/tmp/rdb_tmp get DOES_NOT_EXIST 2>&1 | grep -C 3 'RocksDB option file'
[pid 146611] fread_unlocked(0x7ffcfba382f0, 1, 8192, 0x7fc4e844e780 <unfinished ...>
[pid 146611] fstat@SYS(3, 0x7ffcfba380f0) = 0
[pid 146611] mmap@SYS(nil, 4096, 3, 34, -1, 0) = 0x7fc4eaee0000
[pid 146611] read@SYS(3, "# This is a RocksDB option file."..., 8192) = 4252
[pid 146611] read@SYS(3, "", 4096) = 0
[pid 146611] <... fread_unlocked resumed> ) = 4252
[pid 146611] feof(0x7fc4e844e780) = 1
```
Closes https://github.com/facebook/rocksdb/pull/3294
Differential Revision: D6653684
Pulled By: ajkr
fbshipit-source-id: 222f25f5442fefe1dcec18c700bd9e235bb63491
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| buckifier | ||
| build_tools | ||
| cache | ||
| cmake | ||
| coverage | ||
| db | ||
| docs | ||
| env | ||
| examples | ||
| hdfs | ||
| include/rocksdb | ||
| java | ||
| memtable | ||
| monitoring | ||
| options | ||
| port | ||
| table | ||
| third-party | ||
| tools | ||
| util | ||
| utilities | ||
| .clang-format | ||
| .gitignore | ||
| .travis.yml | ||
| appveyor.yml | ||
| AUTHORS | ||
| CMakeLists.txt | ||
| CODE_OF_CONDUCT.md | ||
| CONTRIBUTING.md | ||
| COPYING | ||
| DEFAULT_OPTIONS_HISTORY.md | ||
| DUMP_FORMAT.md | ||
| HISTORY.md | ||
| INSTALL.md | ||
| issue_template.md | ||
| LANGUAGE-BINDINGS.md | ||
| LICENSE.Apache | ||
| LICENSE.leveldb | ||
| Makefile | ||
| README.md | ||
| ROCKSDB_LITE.md | ||
| src.mk | ||
| TARGETS | ||
| thirdparty.inc | ||
| USERS.md | ||
| Vagrantfile | ||
| WINDOWS_PORT.md | ||
RocksDB: A Persistent Key-Value Store for Flash and RAM Storage
RocksDB is developed and maintained by Facebook Database Engineering Team. It is built on earlier work on LevelDB by Sanjay Ghemawat (sanjay@google.com) and Jeff Dean (jeff@google.com)
This code is a library that forms the core building block for a fast key value server, especially suited for storing data on flash drives. It has a Log-Structured-Merge-Database (LSM) design with flexible tradeoffs between Write-Amplification-Factor (WAF), Read-Amplification-Factor (RAF) and Space-Amplification-Factor (SAF). It has multi-threaded compactions, making it specially suitable for storing multiple terabytes of data in a single database.
Start with example usage here: https://github.com/facebook/rocksdb/tree/master/examples
See the github wiki for more explanation.
The public interface is in include/. Callers should not include or
rely on the details of any other header files in this package. Those
internal APIs may be changed without warning.
Design discussions are conducted in https://www.facebook.com/groups/rocksdb.dev/