You mention on bug 22624 the possibility of normalising the entire archive table to MW 1.5+ format. What are the chances of moving them back to revision and use revdelete for all deletions (removing archive table)? See bugs 18104, 21279, 18780.

Aryeh Gregor wrote: That compression scheme was called CGZ. It helped quite a lot, saving 85% or so compared to uncompressed plain text, IIRC. But the script used to do that compression (compressOld.php) was not compatible with $wgDefaultExternalStore, so it hasn't been run since 2005. Also it was single-threaded so it would have taken a very long time to complete. The new compression script (recompressTracked.php) works with $wgDefaultExternalStore and various other storage type subtleties. It copies all text from a given set of source clusters to a single destination cluster, allowing the original clusters to be deleted. This is handy from a sysadmin perspective. Also, recompressTracked.php is scaled up in various ways: it runs multiple worker processes in parallel, it's restartable, and it uses transactions to guarantee data integrity even if other processes are updating the same rows at the same time, or if the worker process is killed at any time. The maximum dictionary size for gzip is 32KB. It was easy to see that the compression ratio in the CGZ scheme worsened dramatically once the article size exceeded 32KB, because subsequent revisions were no longer able to reference text in previous revisions. We have a lot more articles over 32KB in Wikipedia today, so the compression ratio would not have been as good as it was back in 2005. The DiffHistoryBlob project was interesting, and achieved awesome compression ratios compared to CGZ. But it was relatively straightforward. Most of the work to make this happen was in the development and operation of trackBlobs/recompressTracked. -- Tim Starling