Bacula 一個提供備份 Solution 的 Open Source Project
http://www.bacula.org/
裡面主要分成五個部份:
– Director 負責 Backup/Restore/Verify 和 Archive 這幾個動作,它是 Daemon.
– Console 用來跟 Director 溝通的 Interface
– Files Client Program,也是一個 Daemon, 負責提供檔案屬性跟 Director所需的資料.
– Storage 負責讀/寫你的 Tape 或其他媒體.
– Catalog 維護索引或 Volume Database.
架構圖:
安裝請依照慣例的 ./configure, make, make install 三部曲即可
安裝完成以後,測試 conf 檔案是否有問題:
#bacula-dir -t
#bacula-fd -t
#bacula-sd -t
#console -t
如果想讓 bacula daemon 在開機時自行啟動的話:
#make install-autostart
只裝 File Daemon(Client) 的話,用:
#make install-autostart-fd
主要設定都在 bacula-dir.conf 裡面
可以定義 Storage, Schedule, Job….等等資訊.
bacula-sd.conf 主要定義 Storage, Device 相關資訊.此處需要跟 bacula-dir.conf 中的 Storage 相配合.
bacula-dir.conf
FileSet{} 定義需要備份的目錄或檔案.
Storage{}表示要放Archive 的地方.
Schedule{} 定義執行的排程.
Job{} 則定義工作,裡面則會用到前面所提到的 FileSet, Storage, Schedule 等設定.也可以在執行的前後先執行 Script或程式(RunAfterJob, RunBeforeJob).
還可以設定 Job, Volume …等的保留時間( Retention ).
另外也支援自動換片的 Device, 只要在 Device {} 裡面指定 Change Command = /sbin/xxxx
換片的指令即可.
提供的 PDF 文檔非常詳盡,有兩百多頁~~
也支援 Windows 的 File Daemon(Client Program)
看完以後
覺得整個架構很清晰
也蠻便於管理的~
只是很多東西都必須在 conf 檔中定義好
而無法利用 Client 程式動態的指定Job, Schedule, FileSet …等~
rpm-update
網址:http://www.kleemann.org/rpm-update/
如果你因為不想去 Red Hat 而不使用 up2date,那麼,你可以試試這個程式.
目前最新的版本是 20030102 這個版本.
網站除了 Source 之外,也提供 rpm 可以下載.
(其實也沒有什麼 Source 不 Source 的,因為它是用 Python 寫的)
下載之後,使用 rpm -ivh rpm-update-1-20030102.noarch.rpm 安裝~
安裝應該會很順利,rpm檔裡面只有一個檔案而已.
ok~那麼怎麼使用呢??
先建立此目錄 /var/cache/rpm-update, 因為後面其實會用到此目錄.
但作者可能忘記了.
用 rpm-update -l 列出所有的站台,它是到 Red Hat 網站把 mirror 的網頁抓下來,然後把所有的ftp位址都 grep 出來.
知道位址之後,就可以下載啦~
用 rpm-update -d –host linux.sinica.edu.tw –single 下載
-d 是指 download
–host 是指定位址
–single 則是請 rpm-update 依據目前電腦的 ix86 去抓檔案,如 i386, i686…等等~
用 rpm-update -r –single 進行分析,並列出報告
-r 是指 report
最後,當然就是用 rpm-update -i –single 進行安裝啦.
如果你懶得打那麼多指令
你也可以編輯 ~/.rpm-update/default 這個檔案
把選項都放進去,如:
host = linux.sinica.edu.tw
single
version = 7.3
以後 rpm-update 的時候,就不需要打 –host, –single,直接打 rpm-update -d, rpm-update -r…就行了
安裝完了,不想保留那些 rpm 檔案的話
可以用 rpm-update -c 把 rpm 檔案清除掉.
要讓它自動定期去尋找更新的 rpm,當然也可以放在 crontab 裡面
作者提供了一個不錯的用法:
(rpm-update -d && rpm-update -r) | mail -s “RPM Update” yourname@yourdomain.com
這樣子就行了.
Journaling File Systems
原文出自http://www.linux-mag.com/2002-10/jfs_01.html,本文僅做筆記摘錄,並翻譯摘錄部分.
Linux now offers four alternatives to Ext2: Ext3, ReiserFS, XFS, and JFS.
Linux 現在提供四種不同於 Ext2 的選擇: Ext3, ReiserFS, XFS, and JFS.
They supports journaling, a feature certainly demanded by enterprise, can simplify restarts, reduce fragmentation, and accelerate I/O.
她們都支援日誌(journaling),一個企業級所需的特色,它可以簡單的重新啟動,減少碎裂(fragmentation)和加速I/O.
Some vernacular of file systems:
一些關於 file systems 的常用語:
A “logical block” is the smallest unit of storage, measured in bytes, and it may take several blocks to store a single file.
一個 “logical block” 是 Storage 中最小的單位,以bytes作單位,而通常一個檔案會花好幾個 block 來存放.
A “logical volume” can be a physical disk or some subset of the physical disk space.
一個 “logical volume” 可以是一個邏輯磁碟或實體磁碟空間的集合.
“Block allocation” is a method of allocating blocks where the file system allocates one block at a time.
“Block allocation”:索取 block 的方法.
“Internal fragmentation” occurs when a file does not a fill a block completely.
“Internal fragmentation” 內部碎列,當有很多 block, 而每個 block 都沒有完全塞滿時.
“External fragmentation” occurs when the logical blocks that make up a file are scattered all over the disk.
“External fragmentation” 外部碎列,當一個檔案分散在很多且不同的 block 上時.
An “extent” is a large number of contiguous blocks. described by a triple, consisting of (file offset, starting block number, length), where file offset is the offset of the extent’s first block from the beginning of the file, starting block number is the first block in the extent, and length is the number of blocks in the extent. For large files, extent allocation is a much more efficient technique than block allocation.
“extent” 一堆連續的 blocks, 包含 file offset, starting block number, length. file offset 就是相對於檔案的位址, starting block number 就是起始的 block 號碼, length 就是 block 的數目.
“meta-data” is the file system’s internal data structures. Meta-data includes date and time stamps, ownership information, file access permissions, other security information such as access control lists (if they exist), the file’s size and the storage location or locations on disk.
“meta-data” 就是 file system 的內部資料結構. 包含日期和時間戳記,擁有者,存取權限以及其他安全性資訊,檔案長度,和位置…
An “inode” stores all of the information about a file except the data itself. as a “bookkeeping” file for a file. An inode contains file permissions, file types, and the number of links to the file. It can also contain some direct pointers to file data blocks; pointers to blocks that contain pointers to file data bocks (so-called indirect pointers); and even double- and triple-indirect pointers. Every inode has a unique inode number.
“inode” 儲存檔案除了資料以外的所有資訊. 每個 inode 都有一個獨一無二的號碼.
A “directory” is a special kind of file that simply contains pointers to other files. Specifically, the inode for a directory file simply contains the inode numbers of its contents, plus permissions, etc.
“directory” 一種特殊的檔案,簡單的包含其他檔案的指標.當然也有 inode 和存取權限等資訊.
Corruption occurs because the logical operation of writing (or updating) a file is actually a sequence of I/O, and the entire operation may not be totally reflected on the media at any given point in time.
錯誤的發生是因為寫入(或更新)檔案的邏輯動作是循序的 I/O 動作,而這整個動作並未完全地反映到實際媒體上.
The magic of journaling file systems lies in transactions.
Journaling file system 的魔法是依賴於 transaction 之上.
treats a sequence of changes as a single, atomic operation.
就像是一個循序的改變,如同一個單一,極微的動作.
tracks changes to file system meta-data and/or user data.
追蹤 file system meta-data 和(或)使用者資料的變化.
The journal in a journaling file system is simply a list of transactions.
Journal 在 journaling file system 簡單的說就是一個 transaction 的列表.
In the event of a system failure, the file system is restored to a consistent state by replaying the journal.
在系統發生錯誤時,file system 就依照目前的狀態,回頭播放一次 journal.
inspects only those portions of the meta-data that have recently changed.
審查這些 meta-data 有被變動過的部份.
also address another significant problem: scalability.
但也有另外一個值得注意的問題: scalability 可靠性.
Features of modern file systems include:
現代檔案系統的特色:
– Faster allocation of free blocks. Extents (as described above) and B+ trees are used individually or together to find and allocate several free blocks, either by size or location, quickly.
快速地配置. Extents 和 B+ trees 被單獨(或一起)用來快速地尋找和配置數個閒置的 block.
– Large (or very large) numbers of files in a directory.
在一個目錄中能存在大量或很大量的檔案.
– Large files.
大量的檔案.
Ext3
designed to provide higher availability without impacting the robustness (at least the simplicity and reliability) of Ext2.
被設計來提供高可用度而使得 Ext2 不需面對太強的衝擊.
uses the same disk layout and data structures as Ext2, and it’s forward- and backward-compatible with Ext2
使用和 Ext2 相同的 disk 配置和資料結構, 而且它可以向前或向後相容於 Ext2.
limitations that Ext2 has. The fixed internal structures of Ext2 are simply too small (too few bits) to capture large file sizes, extremely large partition sizes, and enormous numbers of files in a single directory. Moreover, the bookkeeping techniques of Ext2, such as its linked-list directory implementation, do not scale well to large file systems (there is an upper limit of 32,768 subdirectories in a single directory, and a “soft” upper limit of 10,000-15,000 files in a single directory.)
限制和 Ext2 相同.固定的Ext2內部結構太小(太少bits),且使用的 Link list 在大磁碟環境下表現不佳.
Switching to Ext3
# tune2fs -j /dev/hdb3
Ext3 provides three data journaling modes that can be set at mount time: data=journal, data=writeback, and data=ordered. The data=journal mode provides both meta-data and data journaling. data=writeback mode provides only meta-data journaling. data=ordered mode, which is the default mode, provides meta-data journaling with increased integrity.
提供三種模式: data=journal(保護最完整), data=writeback(只保護 meta-data), data=ordered(預設,保護 meta-data之外,即較完整的journaling).
By the way, the 2.4 kernel has a limit of 2048 Gb for a single block device, so no file system larger than that can be created at this time (without patching the standard kernel). This restriction could be removed in the 2.5.x development kernel, and there are patches available to remove this limit, but as of 2.5.29, the patches haven’t been officially included yet.
目前 2.4 仍然有 2048Gb 的限制.
ReiserFS
One of the unique advantages of ReiserFS is support for small files — lots and lots of small files.
比較大的特色是支援小檔案,很多很多的小檔案.
ReiserFS is about eight to fifteen times faster than Ext2 at handling files smaller than 1K.
在處理很多小於1k的檔案時,它比 ext2 快七到八倍.
ReiserFS can actually store about 6% more data that Ext2 on the same physical file system.
在和 Ext2 相同的情況下,她也可以存比 Ext2 多 6% 的資料.
ReiserFS can allocate the exact space that’s needed. A B* tree manages all file system meta-data, and stores and compresses tails, portions of files smaller than a block.
只配置實際所需的空間. 使用了 B* tree 管理.
also has excellent performance for large files, but it’s especially adept at managing small files.
同時也對大檔案有很好的效能,但他特別適合用來處理小檔案.
JFS
JFS uses many advanced techniques to boost performance, provide for very large file systems,
使用了很多先進的技術來加速.
SGI’s XFS (described next) has many similar features. Some of the features of JFS include:
XFS 也用了相似的技術. 這些技術包含了:
– Extent-based addressing structures. along with aggressive block allocation policies to produce compact, efficient, and scalable structures for mapping logical offsets within files to physical addresses on disk. This feature yields excellent performance.
Extent-based 定址的資料結構.
– Dynamic inode allocation. JFS dynamically allocates space for disk inodes as required, freeing the space when it is no longer required. Additionally, this feature decouples disk inodes from fixed disk locations.
動態的 inode 配置.自動配置所需的空間,並釋放不需要的空間.
– Directory organization. Two different directory organizations are provided: one is used for small directories and the other for large directories.
目錄的組織,使用了不同的目錄組織來分別處理大的和小個檔案.
– 64-bits. JFS is a full 64-bit file system. This allows JFS to support large files and partitions.
64-bits. 完全的 64-bit file system.
– such as allocation groups (which speeds file access times by maximizing locality), and various block sizes ranging from 512-bytes to 4096-bytes (which can be tuned to avoid internal and external fragmentation).
還有,配置群組及可變動的 block-size.
XFS
A single XFS file system can be 18,000 petabytes (that’s 1015 bytes) and a single file can be 9,000 petabytes. XFS is also capable of delivering excellent I/O performance.
一個單一個 XFS file system 最大可以到 18,000 petabytes 和單一檔案可達 9,000 petabytes. 同時也有能力提供最好的I/O效能.
uses many of the same techniques found in JFS.
使用了許多和 JFS 相同的技術.
8051 概論
CPU - RAM 128 bytes Flash 4k Processor 20Mhz Interrupt 2 Timer 2 I/O 16 bit
記憶體概圖 +------------+ |Jump begin | +------------+ |Jump Timer 0| +------------+ |Int 0(UART) | +------------+ |Jump Timer 1| +------------+ |.... | |.... | +------------+ Notice:每顆 51 不一定都一樣
事件發生時, Interrupt 或 Timer 會去向量找到相關的位址,然後 jump 過去.
程式 always 執行中,不會停. 通常 begin 都只有作 initialize. 當 timer 要觸發或被 interrupt 了,才作事.
vsftpd Overview
網址: http://vsftpd.beasts.org
vsftpd 她是目前號稱最安全的 FTP Server.
也是目前 Red Hat 8, Open BSD, Suse 所採用的 ftp server.
最新的版本是 1.1.3.
下載 tarball 以後,解開~
她不需要特別 configure, 只需要 make, make install 就可以了
make會自動安裝到 /usr/local/sbin 下面去~
而 conf 檔,則需要自行把 tarball 內附的 vsftpd.conf 複製到 /etc 去才行.
預設的 Server Type 是 inetd, 而不是 Standalone 型態~
所以你需要用 kill -HUP xinetd-pid
來請求 xinetd 重新載入 configuration.
預設的 Configuration 也很安全,完全不讓人登入,也不讓你寫入….非常的…嗯…安全~
你需要在 vsftpd.conf 裡面修改這幾個設定才能讓一般的使用者能登入並擁有寫入的權限:
local_enable=YES
write_enable=YES
如果要讓他以 Standalone 型態起來,則可以在設定裡面置入
listen=YES
並在 /etc/rc.d/init.d 裡面放 script 就行了
至於其他的設定,可以自行用 man vsftpd.conf 來找到用法.
和 proftpd 比較起來
設定是簡單了許多
蠻有那種樸實無華的味道~
再加上檔案又小~
沒什麼可以挑剔的~
期待 2.0 吧
2.0 的 beta 已經 release 了~
相信正式版應該很快就會 Release.
National Storage Day 2 Digest
Introduction:
一開始
何麗玲,HP現任董事長就出來致詞~
來賓出來拋磚~
大致提到:
Adaptive Storage Infrastructure 一個漸進式的 Storage 架構,而非急進的,意思就是你可以慢慢買,再加上去.
還有 New Storage Architectures 的一些特性,
1.Cheap Storage
2.Fleshing out internet application
3.Storage intensive data types
4.Grow
…
主要的 issue,
1. Managing risk
2.資料的成長比 Storage 的預期增加速度要快.
…
“…”表示是抄漏的,到時候要去下載研討會簡報才知道.
ENSA eXtended
接著就是 HP 的Storage處的處長出來介紹 HP 的 ENSA eXtended
蔣先生提到 1998 年 HP 就已經提出 ENSA, 而在這幾年,也都一一實現了
ENSA 主要的定義是:
– Modularity
– Scalability
– Available
而新的 ENSA eXtended 則是
以 an open adaptive storage infrustructure 作為架構,有 Controllable, Resilient(快速復原), Extensible 這三個特性
這裡是我手繪的圖形:
不過畫的不是很好,同樣以後也可以直接參考上面提供的網址去下載簡報來看.
詳情網址: http://www.hp.com/go/ENSAextended/
在即將中午的時候
又有提到 HP Utility Data Center,這個時候已經快睡著了 icon_sad.gif
UDC 有以下的特性:
1.Write Once
2.Resource virtualization
3.Utility Controller
主講人因為有被交代不可以耽誤大家用餐時間,所以講的很快
詳情網址: http://www.hp.com/large/infrastructure/utilitydata/overview/
吃完中餐
就是下午的議程了
下午分成四個 Track: A, B, C, D
我選擇 A1, D2, C3
A1
主要 topic:
1. What’s virtualization?
2. Array level virtualization.
3. Storage Level virtualization.
這邊的大意就是:
把所有的 Storage 集中為一個 pool, 對外只公開一個 Interface, 別人只要透過這個 Interface 就可以取得所需的空間,而增減只在這個 pool 中增減,不影響其他的機器.甚至在這個 Storage pool 和要存取的 Server 中間,再加上適當的 switch, 及佈線,就可以達到互相支援及 Balance 的功能.
好處:
– Increase disk utilization
– Reduce operational burden
– Eliminate costly downtime
– enhance performance
另外有提到 FSAM, 她是一個 Storage vision, 主要討論如何有效集中管理 Storage.
這個 Virtualization 的核心技術就是 SAN, 使用 Server & Storage Technology.
最後有日光星的 CIO 說明為什麼會使用此技術,還有就是主講人提供一個以色列公司的 Flash 動畫,很生動地把她所要說的課題表達出來.
D2. Continuity Plan( Disaster Recovery)
p.s.這堂課很多人去聽,差點擠不進去.
當發生意外狀況時,對 IT 而言是損失設備和資料,對企業而言是 business process.企業這邊他舉了一個榮總的例子,說榮總有一次電腦壞掉,然後一堆人就不會使用人工繼續作業了.
而 Continuity Plan Plan 就是使損失降到最低.
Definition:
HA – High available.
DR – Disaster Recovery
DT – Disaster Tolerance
BC – Business Continuity
BC = HA DR DT
考慮 downtime is not acceptable,最大的原因是企業朝向國際化邁進,因為時差之故,所以不能被接受.要如何減低??
Downtime is controllable.
Perspective:
– Ensure 事件不變成災難.
– 包含 Broad spectrum of business and technology issue.
– 達到最高可用度.
一般而言有十個步驟來練習/規劃,稱
Professional Practice for Continuity Planning:
Step 1~3 是 Preplanning
Step 4~6 Planning
Step 7~10 Post planning
而 Step 9~10 是 Optional 的,視行業及公司狀況而定,或者連絡外面的機構.
Planning Model 和 CMMI Model 相似,但 execution 是在狀況發生時才執行,同樣也是一個 Cycle, 規劃 -> 模擬演練 -> 測試 -> …..
在 Plan 擬訂出來之後,仍要適當的評估,以期能使用最適當的 cost 來得到最好的 benefit.
另外人員的食宿也要考量.
C3.
我有點後悔去聽這堂課,主要介紹 CA ARC Server v9.
不過有把幾個專業名詞抄了下來:
Online storage – always standby 給人存取的 storage.
Nearline storage – 如: MO, 光碟櫃…等,可以 random access, 但並非經常存取,存放在這裡的資料稱作 Inactive Data.
Offline storage – 主要是 tape, autoloader…..
結論:
HP 以及其協力廠商的一個 storage solution show.
相關網址:
National Storage Day 網址:
http://gate.erapr.com/event/hpstorageday/
研討會簡報下載位址:
http://gate.erapr.com/event/hpstorageday/news.html
HashGen
前幾天發現一個有趣的專案: Hashgen, http://www3.sympatico.ca/vladimir.shiryaev/hashgen/
編譯之後
發現它是一個可以把字典檔變成 C/C 的 Hash 搜尋 function / Class.
產生出來的原始碼效率很好!
看過程式以後,了解他首先把字典檔變為陣列,再找出適當的 Hash 大小,並宣告陣列來存放 Hash 的資料,也因此效率很好~~
用法很簡單
1.先建立字典檔.一行一個單字,命名為 mydict,如
the
pencil
pen
keyword
…
2.執行 hashgen -T testme.c -o myhash.h mydict 之後,就會產生 testme.c 和 myhash.h 了,此時你就可以進行編譯.
如果要產生 C 的 code, 就用 hashgen -T testme.c -l c -o myhash.h mydict
這裡介紹的只是一個簡單的用法,裡面還有更多參數,可以讓你指定 hash value…等等的~
更進階的用法:
你也可以在字典檔中指定 hash value
用法是使用 [ declarations ] 和 [ entries ] 這 2 個 section
如
[ options ]
entry-struct-name=TokenEntry
[ declarations ]
struct TokenEntry {
const char* name;
const char* value;
};
[ entries ]
pen, “this is my pen”
pencil, “this is my pencil”
book, “this is my book”
限制:
雖說 key 的字串長度,可以無限長,但在此只有前 32 個字元會被用來 hashing.
當 keyset 大於 3000 個的時候,有可能會因此而變慢.
目前還沒有想到比較好的應用方法
似乎只適合用在字典固定的場合,而不適用於動態增加的場合.
VFP Toolkit for Visual Studio.NET
其實他根本就是一個 wrapper
把 .net 的 code 給包裝起來
看起來的確變的很類似 vfp
但實際上宣告變數以及語法仍然遵循 c# 或 vb.net
而非原來的 vfp
不過文件上說的沒錯
他提供了絕大部分的 vfp 函數
可是~
存取資料時
仍然要使用 sqlconnect
而不是 use
也因此沒有索引的功能
但有提供索引搜尋跟切換索引的功能
只是這些東西仍然依存於 .net dataview 元件的能力
換言之
如果要細調其執行效能
恐怕仍然需要了解 .net ado.net
source code 很有幫助,並不是很困難
建議也下載回去看
對上手 .net 有相當的助益
VFP OLEDB Drivers How-To
限制:
以6.0而言,似乎一定要用 ado 來開啟
範例:
OConn = CREATEOBJECT(“ADODB.Connection”)
OConn.ConnectionString = “provider=vfpoledb.1;;
data source=.\testdbc.dbc”
OConn.Open
語法:
Provider = VFPOLEDB
Data Source=cPath
Specifies the path to the Visual FoxPro database or folder containing free tables. For example, d:\vfp7\samples\data\testdata.dbc
Mode=cMode
Specifies one of the following: Read, ReadWrite, Share Deny None (default), Share Deny Read, Share Deny Write, Share Exclusive (inclusive of the previous two modes).
可以丟如下指令
The Visual FoxPro OLE DB Provider supports the native Visual FoxPro language syntax for the following commands:
CREATE TABLE – SQL Command
Creates a table having the specified fields.
DELETE – SQL Command
Marks records for deletion.
DROP TABLE Command
Removes a table from the database specified with the data source and deletes it from disk.
INSERT – SQL Command
Appends a record to the end of a table that contains the specified field values.
SELECT – SQL Command
Retrieves data from one or more tables.
UPDATE – SQL Command
Updates records in a table with new values.
The Visual FoxPro Language Reference contains detailed information about the following supported commands:
ALTER TABLE – SQL Command
Programmatically modifies the structure of a table.
CREATE TABLE – SQL Command
Creates a table having the specified fields.
Using Data Definition Language (DDL)
You cannot include DDL in the following places:
In a batch SQL statement that requires a transaction
Following a previously executed statement that required a transaction if not in auto-commit mode and if your application has not yet called SQLTransact.
For example, if you want to create a temporary table, you should create the table before you begin the statement requiring a transaction. If you include the CREATE TABLE statement in a batch SQL statement that requires a transaction, the provider returns an error message.
DELETE – SQL Command
Marks records for deletion.
DELETE TAG Command
Removes a tag or tags from a compound index (.cdx) file.
DROP TABLE Command
Removes a table from the database specified with the data source and deletes it from disk.
INDEX Command
Creates an index file to display and access table records in a logical order.
INSERT – SQL Command
Appends a record to the end of a table that contains the specified field values.
SELECT – SQL Command
Retrieves data from one or more tables.
The Visual FoxPro OLE DB Provider supports the native Visual FoxPro language syntax for this command.
SET ANSI Command
Determines how comparisons between strings of different lengths are made with the = operator in Visual FoxPro SQL commands.
SET BLOCKSIZE Command
Specifies how disk space is allocated for the storage of memo fields.
SET COLLATE Command
Specifies a collation sequence for character fields in subsequent indexing and sorting operations.
SET DELETED Command
Specifies whether records marked for deletion are processed and whether they are available for use in other commands.
SET EXACT Command
Specifies the rules for comparing two strings of different lengths.
SET EXCLUSIVE Command
Specifies whether table files are opened for exclusive or shared use on a network.
SET NULL Command
Determines how null values are supported by the ALTER TABLE – SQL, CREATE TABLE – SQL, and INSERT – SQL commands.
SET PATH Command
Specifies a path for file searches.
Provider Remarks
If you issue SET PATH in a stored procedure, it will be ignored by the following functions and commands: SELECT, INSERT, UPDATE, DELETE, and CREATE TABLE
If you issue SET PATH in a stored procedure and do not subsequently set the path back to its original state, other connections to the database will use the new path (because SET PATH is not scoped to data sessions).
If you want to create, select, or update tables in a directory other than that specified by the data source, specify the full path of the file with your command.
SET REPROCESS Command
Specifies how many times or for how long to lock a file or record after an unsuccessful locking attempt.
SET UNIQUE Command
Specifies whether records with duplicate index key values are maintained in an index file.
UPDATE – SQL Command
Updates records in a table with new values.
C++ ABI
ABI 是 Application Binary Interface, 它是一種介於使用者 C++ 程式碼和提供實作系統和 library 的物件程式碼.
這包含了 C++ 資料物件的記憶體配置,包含先行定義和使用者定義的資料型態,也包含了內部 Compiler 產生的物件,如: virtual tables.
它也包含了函數呼叫介面,例外處理介面,全域名稱空間和多樣物件程式碼的協定.
GCC 將在 3.2 版以後為編譯器提供此功能~