The S3 applier makes use of the JavaScript based batch loading system (see Section 5.6.4, “JavaScript Batchloader Scripts”). This constructs change data from the source-database. The change data is then written into csv files, optional compressed, and loaded into an S3 bucket.
The full replication of information operates as follows:
Data is extracted from the source database using the standard extractor, for example by reading the row change data from the binlog in MySQL.
The Section 11.4.5, “ColumnName Filter” filter is used to extract column name information from the database. This enables the row-change information to be tagged with the corresponding column information. The data changes, and corresponding row names, are stored in the THL.
The Section 11.4.31, “PrimaryKey Filter” filter is used to extract primary key data from the source tables.
On the Applier replicator, the THL data is read and written into batch-files in the character-separated value format.
The information in these files is change data, and contains not only
the original row values from the source tables, but also metadata
about the operation performed (i.e.
INSERT,
DELETE or
UPDATE, and the primary key of
for each table. All UPDATE
statements are recorded as a
DELETE of the existing data,
and an INSERT of the new data.
In addition to these core operation types, the batch applier can also
be configured to record UPDATE
operations that result in
INSERT or
DELETE rows.
The staging files created by the replicator are in a specific format that incorporates change and operation information in addition to the original row data.
The format of the files is a character separated values file, with
each row separated by a newline, and individual fields separated by
the character 0x01.
The content of the file consists of the full row data extracted from the Source, plus metadata describing the operation for each row, the sequence number, and then the full row information.
| Operation | Sequence No | Table-specific primary key | DateTime | Table-columns... |
|---|---|---|---|---|
| OPTYPE |
SEQNO that generated this row
| PRIMARYKEY | DATATIME of source table commit |
The operation field will match one of the following values
| Operation | Description | Notes |
|---|---|---|
| I |
Row is an INSERT of new
data
| |
| D |
Row is DELETE of existing
data
| |
| UI |
Row is an UPDATE which
caused INSERT of data
| |
| UD |
Row is an UPDATE which
caused DELETE of data
|
For example, the MySQL row from an
INSERT of:
| 3 | #1 Single | 2006 | Cats and Dogs (#1.4) |
Is represented within the CSV files generated as:
"I","5","3","2014-07-31 14:29:17.000","3","#1 Single","2006","Cats and Dogs (#1.4)"
The character separator, and whether to use quoting, are configurable within the replicator when it is deployed. For S3, the default behavior is to generate quoted and comma separated fields.
As the target for the Amazon S3 Applier is not a relational database in the sense of traditional Tungsten replication, the replicator stores it's apply position as a JSON structure on the local filesystem.
This allows the replicator to know it's starting position in the case of a restart.
The file is located in the following directory: /opt/continuent/metadata/applier/
and is called serviceNamecommitseqno.0
The contents of the file will look something like the following, and should NOT be edited unless advised to do so by Continuent Support
{
"sourceId" : "ext01",
"epochNumber" : "0",
"fragno" : "0",
"eventId" : "mysql-bin.000002:0000000000134613;27",
"seqno" : "427",
"lastFrag" : "true",
"extractedTstamp" : "1687439308000",
"appliedLatency" : "0",
"shardId" : "demo"
}