add new param to device config properties: db connection pool size

connection pool = number of database connections opened when the app opens
a database. These pooled connections are used by readers only and they
use the sqlite write-ahead-logging option to increase reader
concurrency.
The size of this connection pool depends on the number of CPUs, RAM etc.
On most single-core devices, this can be set to 1.
But on some multi-core devices with more RAM, pool size can be
more than 1.
On a device with more resources, here are the results of a test (in
coretests/src/android/database/sqlite/SQLiteDatabaseTest.java)
which measures the reader-parallelism achieved for different connection
pool sizes.
connpool-size = 1
  num xacts by writer = 467
  num-reads-in-xact/NOT-in-xact by reader1 = 1358/14542, by reader2 = 1431/14269
connpool-size = 2
  num xacts by writer = 473
  num-reads-in-xact/NOT-in-xact by reader1 = 5703/35227, by reader2 = 6222/35898
connpool-size = 3
  num xacts by writer = 542
  num-reads-in-xact/NOT-in-xact by reader1 = 6531/32329, by reader2 = 6252/32728
connpool-size = 4
  num xacts by writer = 578
  num-reads-in-xact/NOT-in-xact by reader1 = 6009/32701, by reader2 = 5977/32953
connpool-size = 5
  num xacts by writer = 547
  num-reads-in-xact/NOT-in-xact by reader1 = 6554/31186, by reader2 = 5318/31022
connpool-size = 6
  num xacts by writer = 534
  num-reads-in-xact/NOT-in-xact by reader1 = 5317/31463, by reader2 = 5413/31537
connpool-size = 7
  num xacts by writer = 549
  num-reads-in-xact/NOT-in-xact by reader1 = 5396/28004, by reader2 = 5214/28496

seems like connection pool size of 3 is optimal on this device.

Change-Id: I348ff5a31783c31b5e3e5ac78b7c2cea54ef114a

0 files changed, 0 insertions, 0 deletions