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Questions tagged [wal]

WAL, or write-ahead log, is a form of journalling used as part of crash-safety and atomic commit support in databases like PostgreSQL and SQLite.

PostgreSQL's write-ahead log is a crucial feature that permits crash-safety and atomic commit to be implemented. It's also heavily used in PostgreSQL's point-in-time recovery, streaming replication, and archive based replication features, as well as hot physical backup.

In SQLite, the default method by which SQLite implements atomic commit and rollback is a rollback journal. Beginning with version 3.7.0, a new "Write-Ahead Log" option (hereafter referred to as "WAL") is available.

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What is the checksum algorithm in SQLite WAL

I'm wondering about the checksum algorithm in SQLite WAL mode I already checked doc file but it says like this (this image is captured in sqlite doc file https://www.sqlite.org/fileformat2.html#section_4_1) I didn't understand what is the meaning…
Jong Hyeok Park
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WAL level not sufficient for making an online backup

I have tried to do database replication in linux 7.0 red hat using postgresql. I refered this URL for Confuring http://blog.terminal.com/postgresql-replication-and-backup-methods/ I completed the the steps upto this step Configuring the slave…
Karthik KM
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Postgres slave server log replay details

Postgres supports master slave replication through WAL(Write Ahead Log) files. On master server, a backend process called WALSender will send log files(records) to the slave server, and on the slave server, a backend process called WALReceiver will…
ray6080
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Failed to do checkpoint

int iReturn = sqlite3_wal_checkpoint_v2(m_poDB, NULL, SQLITE_CHECKPOINT_FULL, &iSizeOfWalLog, &iNumOfCheckpointedFrames); returns with iReturn = 5 (SQLITE_BUSY). The writer wakes up now and then, adds or deletes a number of rows to the database,…
Fabian
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Can I use WAL mode in SQLite3 if I use an additional mutex for multiple writers?

http://sqlite.org/wal.html WAL mode is specified for N readers and one writer. It the writer's identity interchangible? For example, I have N writers and an additional mutex. Each writer has to obtain this mutex to be able to write, so there are…
Fabian
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SQLite WAL-mode, in-memory, database with private cache?

I am working on a project which relies on the read snapshot isolation that the WAL journal mode provides in Sqlite. It uses multiple connections to the same database to allow concurrent readers and a single writer. For testing, I would like to use…
skabbes
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SQLite API to determine size of WAL file

Is there any api within SQLite which would return the current size of the WAL journal file? I need to check for its size periodically and perform some actions if it exceeds a certain limit. I am currently using system calls like stat() from my c++…
Obli07vion
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merge two sqlite databases with wal and shm constraints in iOS 7.0

I've read many threads about sqlite database and how to update with wal and checkpoint but I really do not understand despite all the information on Internet. I merge two sqlite databases on a Desktop computer with a Python script but when I put the…
Trichophyton
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Java OutOfMemoryError / OrientDB WAL Flush Task error after importing 2M records into OrientDB

After one of my import scripts had completed importing all data, I tried restarting it to grab any updated data. The first thing it does is grab the most recently updated record: db.select().from(newClass).order('updatedAt…
Garrett
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Background service and UI updates and implementing WAL

In my application, I run a service at 12 each night using an Alarm, everything works as intended. I have three Fragment tabs, each tab has a listview, on click of a list item a detailed view is presented. If a user openes my app at say 11:59…
User3
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Postgres wal archivation delay

I've noticed a lag of archive_command execution. The command is configured to set a flag on arhived segment: archive_command = 'rm pg_xlog/*.backuped ; touch %p.backuped' If I run ls then I see that a lot of segments are not…
raacer
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Compress xlog when restoring postgres db?

For postgres, I used 'pg_dump' to dump a db, then use 'psql' to restore the db at the other sever. I found there are huge volume of WAL logs created at pg_xlog/ which consumed a lot of disk space. Is there any way postgres provides to compress…
Yang
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How to enable WAL (write ahead log) in a C++ program?

I currently have two different processes, one process writes into a database and the other one reads and updates the records in the database that were inserted by the first process. Every time I try to start both processes concurrently the database…
atomic_barf
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How to perform GreenPlum 6.x Backup & Recovery

I am using GreenPlum 6.x and facing issues while performing backup and recovery. Does we have any tool to take the physical backup of whole cluster like pgbackrest for Postgres, further how can we purge the WAL of master and each segment as we can't…
Arslan Khalid
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Cannot enlarge string buffer containing 1073741779 bytes by 596 more bytes while reading from PGReplicationStream in java

I am running into the following problem. I want read WAL in postgres database using logical replication and wal2json plugin, Could you please help me how to resolve this issue? Also I observed that the replication slots after some time became…
lion_pankaj
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