In 2012, there were 5.3 million votes cast in the California primary. Political Data was able to classify the 2.2 million VBM ballots that arrived before election day. Additional VBM ballots arrived on election day. The 2.2 million ballots were 44% Democratic/38% Republican. So far, there are 863k mail-in ballots and these are 44% Democratic/35% Republican. It's still early, but this is good news for Democrats. In 2012, CA-36 the early VBM was 48% Republican/37% Democratic. Right now the returns are 43% Republican/40% Democratic. If election day follows the same pattern as VBM does, Democratic congressman Raul Ruiz should do much better in the primary than he did in 2012.
On the other hand, surveys haven't shown this being a better Democratic year than 2012 and Democrats haven't shown up in special elections so far this cycle. I don't have the data but anecdotes about the San Diego mayoral election indicated Democrats returned early mail in ballots at a better than expected rate. So Democrats could just be mailing in VBM ballots that they would've turned in on election day in previous elections. How 2014 Democratic party vote shares come out on election day will tell us if Democrats are doing better with their primary turn-out problem.