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Overview
Parallel writes is a configurable feature relating to the number of Web service requests across an instance of SkySync, on a given node, that will operate in parallel. It is very important to note that increasing the number of parallel writes does not always equal faster/better transfer performance. There is a long list of concepts that have to be taken into account.
Parallel Writes and Memory Usage
A job in SkySync does not use a fixed amount of memory. Memory usage for individual jobs will vary based on a number of factors, the most significant one is the number of files and how those files are distributed (all in one folder, throughout sub-folders, etc.). To avoid excessive memory usage related to how content is distributed, SkySync recommends preserving the system default for Directory Item Limits | max_items_per_container. The main factors for memory usage for a SkySync node will be number of concurrent jobs + Parallel Writes for the jobs and the memory impact of the specific jobs.
If memory issues occur due to increasing the Directory Item Limit or Parallel Writes, there is no other mitigation other than reducing the number of current jobs or breaking up the source content in to multiple jobs. SkySync will keep using memory until it runs out (it will not self-limit), and it will eventually reach the environment max. Reaching an environment max may result in a non-graceful termination of SkySync that could result in jobs re-transferring files, permissions or metadata. In the case of larger jobs being stopped in this manner, they will enter recovery mode, continue to use all the memory, then get stopped again, in a loop causing a loss of throughput.
Default Parallel Writes
The default parallel write value is set at 4, 8, or 12 based on CPU logical processors count for the machine running the SkySync service.
If the CPU Logical Processors is 2, the default parallel writes value is 4.
If the CPU Logical Processors is 8, the default parallel writes value is 8.
If the CPU Logical Processors is 32, the default parallel writes value is 12.
Changing the Global Parallel Writes
The global parallel writes setting changes the settings for all jobs. If you want to change the setting for a single job, you will need to use the REST API to update the job configuration for the individual job. Refer to Parallel Writes Per Job for more information on updating the parallel writes setting for an individual job. If you have multiple nodes, all nodes will be updated with the new setting.
Select Settings.
Select Performance.
In the Requested field, type the number of parallel writes you want to set.
Select Save.
