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Selama pengambilan data perubahan, Datastream membaca file log redo Oracle untuk
memantau perubahan pada database sumber dan mereplikasinya ke instance
tujuan. Setiap database Oracle memiliki serangkaian file log pengulangan online. Semua
catatan transaksi di database dicatat dalam file. Saat file log redo saat ini dirotasi (atau dialihkan), proses pengarsipan menyalin file ini ke penyimpanan arsip. Sementara itu, database mempromosikan
file lain untuk berfungsi sebagai file saat ini.
Konektor Oracle Datastream mengekstrak peristiwa pengambilan data perubahan (CDC)
dari file log pengulangan Oracle yang diarsipkan.
Mengakses file log redo
Datastream dapat menggunakan Oracle LogMiner API atau metode pembaca biner untuk mengakses file log pengulangan:
Oracle LogMiner: utilitas siap pakai yang disertakan dalam database Oracle.
Jika Anda mengonfigurasi Datastream untuk menggunakan Oracle LogMiner API, Datastream hanya dapat bekerja dengan file log pengulangan yang diarsipkan, file log pengulangan online tidak didukung.
Metode LogMiner API bersifat berutas tunggal dan tunduk pada latensi yang lebih tinggi dan
throughput yang lebih rendah saat bekerja dengan database sumber dengan jumlah transaksi yang besar.
LogMiner mendukung sebagian besar jenis data dan fitur database Oracle.
Pembaca biner (Pratinjau):
utilitas berperforma tinggi khusus yang berfungsi dengan file log redo online dan yang diarsipkan. Pembaca biner dapat mengakses file log menggunakan Pengelolaan Penyimpanan Otomatis (ASM) atau dengan membaca file secara langsung menggunakan objek direktori database.
Pembaca biner bersifat multithread dan mendukung CDC latensi rendah. Hal ini juga berdampak rendah pada database sumber karena log redo diuraikan di luar operasi database. Metode CDC pembaca biner memiliki dukungan terbatas untuk jenis atau fitur data tertentu. Untuk mengetahui informasi selengkapnya, lihat
Batasan umum.
Menetapkan parameter konfigurasi untuk file log pengulangan Oracle
Desain ini memiliki implikasi besar pada potensi latensi Datastream. Jika file log pengulangan Oracle sering diganti atau dipertahankan dalam ukuran yang lebih kecil (misalnya, < 256 MB), Datastream dapat mereplikasi perubahan dengan lebih cepat.
Ada parameter konfigurasi yang dapat Anda tetapkan untuk mengontrol frekuensi rotasi file log:
Ukuran: File log pengulangan online memiliki ukuran minimum 4 MB, dan ukuran default bergantung pada sistem operasi Anda. Anda dapat mengubah ukuran file log dengan membuat file log online baru dan menghapus file log yang lebih lama.
Untuk menemukan ukuran file log pengulangan online, jalankan kueri berikut:
SELECTGROUP#,STATUS,BYTES/1024/1024MBFROMV$LOG
Waktu: Parameter ARCHIVE_LAG_TARGET memberikan batas atas durasi (dalam detik) rentang log saat ini dari database utama.
Ini bukan waktu peralihan log yang tepat, karena memperhitungkan berapa lama waktu yang dibutuhkan untuk mengarsipkan log. Nilai defaultnya adalah 0 (tanpa batas atas), dan nilai 1800 (atau 30 menit) atau kurang yang wajar disarankan.
Anda dapat menggunakan perintah berikut untuk menetapkan parameter ARCHIVE_LAG_TARGET, baik selama inisialisasi atau saat database aktif:
SHOW PARAMETER ARCHIVE_LAG_TARGET; Perintah ini menampilkan berapa detik yang diperlukan untuk mencakup log saat ini.
ALTER SYSTEM SET ARCHIVE_LAG_TARGET = number-of-seconds; Gunakan perintah ini untuk mengubah batas atas.
Misalnya, untuk menyetel batas atas menjadi 10 menit (atau 600 detik), masukkan ALTER SYSTEM SET ARCHIVE_LAG_TARGET = 600;
[[["Mudah dipahami","easyToUnderstand","thumb-up"],["Memecahkan masalah saya","solvedMyProblem","thumb-up"],["Lainnya","otherUp","thumb-up"]],[["Sulit dipahami","hardToUnderstand","thumb-down"],["Informasi atau kode contoh salah","incorrectInformationOrSampleCode","thumb-down"],["Informasi/contoh yang saya butuhkan tidak ada","missingTheInformationSamplesINeed","thumb-down"],["Masalah terjemahan","translationIssue","thumb-down"],["Lainnya","otherDown","thumb-down"]],["Terakhir diperbarui pada 2025-08-12 UTC."],[[["\u003cp\u003eDatastream utilizes Oracle redo log files to capture changes in source databases and replicate them to the destination instance.\u003c/p\u003e\n"],["\u003cp\u003eDatastream can access redo logs using either the Oracle LogMiner API, which only supports archived files and is single-threaded, or the binary reader method, which supports both online and archived files and is multi-threaded.\u003c/p\u003e\n"],["\u003cp\u003eThe frequency of Oracle redo log file switching, controlled by size and time parameters, significantly impacts Datastream's latency, with smaller, more frequently switched files enabling faster replication.\u003c/p\u003e\n"],["\u003cp\u003eConfiguration parameters, including file size (ideally under 1GB) and the \u003ccode\u003eARCHIVE_LAG_TARGET\u003c/code\u003e parameter (recommended to be 1800 seconds or less), can be adjusted to optimize redo log file rotation for Datastream's performance.\u003c/p\u003e\n"],["\u003cp\u003eWhile manual switching of redo log files via \u003ccode\u003eALTER SYSTEM SWITCH LOGFILE;\u003c/code\u003e is possible for testing, it is not recommended for production due to required privileges and performance impact on the database.\u003c/p\u003e\n"]]],[],null,["# Work with Oracle database redo log files\n\nDuring change data capture, Datastream reads Oracle redo log files to\nmonitor your source databases for changes and replicate them to the destination\ninstance. Each Oracle database has a set of online redo log files. All\ntransaction records on the database are recorded in the files. When the current\nredo log file is rotated (or switched), the archive process\n[copies this file into an archive storage](https://docs.oracle.com/cd/B19306_01/server.102/b14231/archredo.htm#i1006148). Meanwhile, the database promotes\nanother file to serve as the current file.\n\nDatastream Oracle connector extracts change data capture (CDC) events\nfrom **archived** Oracle redo log files.\n\nAccess redo log files\n---------------------\n\nDatastream can use the Oracle LogMiner API or the binary\nreader method to access the redo log files:\n\n- **Oracle LogMiner** : an out-of-the-box utility included in Oracle databases.\n If you configure Datastream to use Oracle LogMiner API, Datastream\n can only work with *archived* redo log files, online redo log files aren't supported.\n The LogMiner API method is single-threaded and is subject to higher latency and\n lower throughput when working with large transaction number source databases.\n LogMiner supports most data types and Oracle database features.\n\n- **Binary reader** ([Preview](/products#product-launch-stages)):\n a specialized, high-performance utility that works with both online and archived\n redo log files. Binary reader can access the log files using Automatic Storage\n Management (ASM) or by reading the files directly using database directory objects.\n Binary reader is multithreaded and supports low-latency CDC. It also creates low\n impact on the source database as redo logs are parsed outside of the database\n operations. The binary reader CDC method has limited support for certain data\n types or features. For more information, see\n [Known limitations](/datastream/docs/sources-oracle#binary-reader-limitations).\n\nSet configuration parameters for Oracle redo log files\n------------------------------------------------------\n\nThis design has profound implications on Datastream's potential latency. If Oracle's redo log files are switched frequently or kept to a smaller size (for example, \\\u003c 256MB), Datastream can replicate changes faster.\n\nThere are configuration parameters that you can set to control the log file rotation frequency:\n\n- **Size:** Online redo log files have a minimum size of 4 MB, and the default size is dependent on your operating system. You can modify the size of the log files by creating new online log files and dropping the older log files.\n\n To find the size of the online redo log files, run the following query: \n\n ```sql\n SELECT GROUP#, STATUS, BYTES/1024/1024 MB FROM V$LOG\n ```\n | Generating very large log files might cause Datastream to time out, which can lead to stream failure. The recommended redo log file size is below 1GB.\n |\n | For information about resizing redo logs for a self-hosted Oracle instance, see [How to resize redo logs in Oracle](https://logic.edchen.org/how-to-resize-redo-logs-in-oracle).\n |\n | For information about resizing redo logs for an Amazon RDS Oracle instance, see [Resizing online redo logs](https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/Appendix.Oracle.CommonDBATasks.Log.html#Appendix.Oracle.CommonDBATasks.ResizingRedoLogs).\n- **Time:** The `ARCHIVE_LAG_TARGET` parameter provides an upper limit of how long (in seconds) the current log of the primary database can span.\n\n This isn't the exact log switch time, because it takes into account how long it will take to archive the log. The default value is `0` (no upper bound), and a reasonable value of `1800` (or 30 minutes) or less is suggested.\n\n You can use the following commands to set the `ARCHIVE_LAG_TARGET` parameter, either during initialization or while the database is up:\n - `SHOW PARAMETER ARCHIVE_LAG_TARGET;` This command displays how many seconds it will take for the current log to span.\n - `ALTER SYSTEM SET ARCHIVE_LAG_TARGET = `\u003cvar translate=\"no\"\u003enumber-of-seconds\u003c/var\u003e`;` Use this command to change the upper limit.\n\n For example, to set the upper limit to 10 minutes (or 600 seconds), enter `ALTER SYSTEM SET ARCHIVE_LAG_TARGET = `\u003cvar translate=\"no\"\u003e600\u003c/var\u003e`;`\n| You can switch the redo log files manually by running the following command:\n|\n| `ALTER SYSTEM SWITCH LOGFILE;`\n|\n| Although using this command is effective for testing purposes, we don't recommend it for production use-cases because of the privileges it requires and the significant performance impact on the database.\n\nWhat's next\n-----------\n\n- Learn more about [Oracle as a source](/datastream/docs/sources-oracle).\n- Learn more about [configuring a source Oracle database](/datastream/docs/configure-your-source-oracle-database)."]]
