On 2014/03/03 23:11, romtek wrote:
Simon, does a real disk have to be a rotating hard disk? Is there problem with SSDs as far as SQLite is concerned?
No, what Simon is trying to point out is simply that the write performance experienced by L. Wood might be because journal writes might be synced to hard disk (in rotating disk cases anyway) and as such cause delays all throughout the transaction even if they are not holding up the final commit. Not because this is in error or wrong in any way, simply as trying to explain why he sees the performance spread he sees.
Other reasons might be excessively large binds causing the cache to spill or simply have memory writes taking so long that it seems to cause inter-transaction delays, although if that were the case one would expect the final commit to take a lot longer even.
My money is still on the specific pragmas used which might be forcing syncs or non-ACID operation. We would need to have the DB schema and the typical query to really test why it works the way it works in his case.
One note on SSD's, they pose no physical problem to SQLite, and in fact works magically fast, but having a DB which read/write a LOT of data on them is not really great since the repeated read-write cycle of specific data areas tire down the typical NAND flash that makes up the SSD, even though modern SSDs may use MLC NAND or have firmware that tries to exercise every bit in memory equally so as to spread the write operations to avoid one piece of disk-memory dying quickly. Eventually though, when all bits of memory experienced upwards of 500K write operations (which is quite a while), it will fail... but you will have lots of warning. A read-only DB on an SSD drive cannot be beaten... even a normal DB where writing does not happen often I would suggest a SSD... but anything with a very active read/write cycle is best avoided - or at a minimum backed up by a good old rotating magnetic platter drive.
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